Removed head and confirmed, 3 9/16 bores indeed, so it's a 235. Which might be ok because 235 parts seem to have greater availability than 261 parts. There's very slight ridge at top of middle two cylinders, will catch a fingernail but the ridge doesn't go all the way around the bore. Outer four cylinders have a trace of carbon, but no ridge that I can feel with a fingernail. Will be doing Hotrod Lincoln's technique of measuring taper pretty soon: https://www.stovebolt.com/techtips/engines/cylinder%20taper/index.html

Got a good recommendation for local machine shop, will likely farm out most of the critical measuring and more. Now that the big question has been answered I'll be taking a slower approach from here on out. Just want a solid reliable engine and will try to keep my bumbling self out of the way in the process to make sure that happens.
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Matthew 6:33

1952 Chevy 1/2-ton 3100
Late '55 235/SM420/torque tube 3.55
Dalton Highway survivor (using original 216)
www.truckwithaheart.com