If Johnston, sends one of his corps on the road to Owl Creek, probably Hardee, as he was the biggest with 3 divisions.
O.R. Vol.X (Correspondences) - pp.370-371 : Hardee's command was initially composed of two divisions from the former Army of Central Kentucky (his own and Pillow's) while G.B. Crittenden's division would have formed the Reserve Corps. Therefore, the three divisions you're counting for Hardee were actually split into two different commands = Hardee's Third Corps and Crittenden's Reserve Corps
Army of the Mississippi, March 29, 1862 (organization as intended by Albert S. Johnston) :
Headquarters
- - - Cavalry Reserve Bde : BG James H. Hawes
First Corps : MG Leonidas Polk (from Dept. No.2, Western Div.)
- 1st Div. : BG Charles Clark
- - - Russell's Bde
- - - Stewart's Bde (from McCown's Command, Island No.Ten)
- 2nd Div. : MG Benjamin F. Cheatham
- - - Johnson's Bde
- - - Stephens' Bde
Second Corps : MG Braxton Bragg
- 1st Div. : BG Daniel Ruggles (from Dept. No.1, New Orleans Defenses)
- - - Pond's Bde
- - - Mouton's / Gibson's Bde
- - - Walker's / Anderson's Bde (split from Walker's Div.)
- 2nd Div. : BG Jones M. Withers (from Dept. Ala. & West Fla., Army of Mobile)
- - - Gladden's Bde
- - - Jackson's Bde
- - - Chalmers' Bde (split from Walker's Div.)
Third Corps : MG William J. Hardee (from Dept. No.2, Army of Central Kentucky)
- - - Reserve (Breckinridge's) Bde
- 1st Div. : BG Thomas C. Hindman
- - - Hindman's Bde
- - - Cleburne's Bde
- 2nd Div. : BG Gideon J. Pillow
- - - Bowen's Bde
- - - Wood's Bde
Infantry Reserve : MG George B. Crittenden (from Dept. No.2, District of East Tenn.)
- - - Carroll's Bde
- - - Statham's Bde
The goal was to create three huge infantry corps, each one supported by cavalry and artillery detachments, and a small reserve division under the least senior Major-General ("a division of not less than two brigades") in order to provide extra punch without depriving any of the main corps.
Unfortunately for Hardee, his corps was nonetheless reduced during the advance preparations on Shiloh and the Reserve was augmented by the transfer of Bowen's Bde and the dissolution of Pillow's Division.
Instead of deploying three infantry corps supported by an infantry division at Shiloh, the Confederates fought as an unbalanced structure of two corps and two divisions (Polk's 8,500 / Bragg's 12,500 / Hardee's 6,500 / Breckinridge's 5,500) while Carroll's Bde and soon-to-be Trapier's Bde were guarding Corinth.
They could hit it from the front with 4 divisions (Clark, Cheatham, Ruggles, and Withers) and flank it with the other 3, you would still have Breckinridge's 3 brigades in reserve in that scenario.
If Hardee had kept control of the whole Army of Central Kentucky, thence his corps would have been composed of three average-to-small divisions while the reserve would consist only of one brigade, under Breckinridge. And Carroll's Bde was left behind to perform garrison duty.
In this case, Hardee's forces are less than ideal to control : three subordinates instead of two may lead to more communication and logistic problems. Moreover, one of these three divisions must leave a brigade at Corinth, while Breckinridge's Bde replaces it and deprives the army of an independent infantry reserve.
My opinion is that the command organization evolved too much between March 5 and April 3, with several disbanded or rearranged formations, which ruined the effectiveness of the army. According to the initial Confederate plans (three-corps structure), I propose below an alternate OOB which might allow the success of such a flanking attack you described :
Army of the Mississippi : Gen. A.S. Johnston = 35,450 INF + 3,000 CAV
Second-in-Command : Gen. P.G.T. Beauregard (could be put in command of an informal wing composed of First and Second Corps)
*First Corps : Maj.-Gen. Polk = 10,000 INF
- 1st Div. : Brig.-Gen. Clark = 4,400 INF
- - - Russell's Bde = 2,100 INF
- - - Stewart's Bde (transferred from McCown's Command) = 2,300 INF
- 2nd Div. : Maj.-Gen. Cheatham = 5,600 INF
- - - B.R. Johnson's Bde = 1,950 INF
- - - Stephens' Bde = 2,200 INF
- - - J.P. Anderson's Bde (transferred from Second Corps) = 1,450 INF
*Second Corps : Maj.-Gen. Bragg = 11,150 INF
- 1st Div. : Brig.-Gen. Ruggles = 4,900 INF
- - - Gibson's Bde = 2,350 INF
- - - Pond's Bde = 2,550 INF
- 2nd Div. : Brig.-Gen. Withers = 6,250 INF
- - - Gladden's Bde = 2,100 INF
- - - J.K. Jackson's Bde = 2,000 INF
- - - Chalmers' Bde = 2,150 INF
*Third Corps : Maj.-Gen. Hardee = 8,150 INF + 3,000 CAV
- - - Hawes' Cavalry Bde = 3,000 CAV
- 1st Div. : Brig.-Gen. Hindman = 4,650 INF
- - - Hindman's Bde = 2,100 INF
- - - Cleburne's Bde = 2,550 INF
- 2nd Div. : Brig.-Gen. Wood = 3,500 INF
- - - Wood's Bde = 1,900 INF
- - - Bowen's Bde = 1,600 INF
*Reserve Division : Brig.-Gen. Breckinridge = 6,150 INF
- - - Carroll's Bde = 2,000 INF (left behind to Corinth)
- - - Statham's Bde = 2,000 INF
- - - Breckinridge's Bde = 2,150 INF
This way, Breckinridge leaves one brigade at Corinth and can support either Polk, Bragg or Hardee during the assault. Hardee's flanking manoeuver can be secured by attaching Hawes' Cavalry Bde to the Third Corps. We now have three corps of approximately 10,000 men each with a smaller reserve of approximately 6,000 men (2,000 of them securing the supply base).
Sidney Johnston could form a three-columns attack with Hardee's troops pushing on the extreme left prededed by a strong cavalry vanguard and flanking both Sherman's Fifth and McClernand First Divisions. Breckinridge can either be deployed behind Hardee to follow early success or behind Bragg to cover the Confederate right. Polk, at the center, will move forward, facing directly the Union positions. However, I'm not sure that these tactical actions can be taken without many difficulties, considering the "terrain" where the units are moving.