Found a guy on eBay who had the buttplate screws that have the 13/32" head diameter - from a m1855-64.
As for the brass band, I know the Sharps carbine, from the earliest serial NM1859s back had brass bands, right? I'll get out my caliper and measure the barrel and forend widths plus overall height as assembled. Maybe the Sharps carbine or long rifle bands will work. I do have all four to try. When I post the specs needed, please check your manufacturer brass band and let me know if a fit, OR if yours would be slightly undersized and could be widened a bit to fit snugly. If the m1855-64 buttplate screws were a match then maybe too the band was shared. Easier to assemble if parts already mass produced for Springfields. Gotta believe Merrill was smart that way.