1955 235 & 261 camshaft specifications on page 154 of the PDF.
1957 261 camshaft specifications on page 177 of the PDF.
From these specs, the only cam differences are in the intake & exhaust ramps.
Maybe the Heritage center links can help you with your other parts questions? I have my learning hat on right now, and am just sending you what I was reading up on. What you're asking is a question for the builder pro's... I'm on the sidelines of a similar swap, so I'm just tracking the info. If the individual parts are identical, they won't know what year engine they're going in.
Brad
