As you probably know, a bellhousing, flywheel and clutch from a 235 will bolt on and work OK- - - -the only real difference in the 235 and the 261 is the bore size- - - -even the crankshaft is identical to a 235. The setup you describe sounds like the engine spent its time in a big rig- - -particularly with the big vacuum connection. The 848 head and valve rotators sound like it's been built up and upgraded a little. 235/261 exhaust valves are identical in head diameter, stem diameter, and length to a small block V8. When rotators were used on the SBC, the exhaust valve springs were about 1/8" shorter in overall length than the intakes to compensate for the thickness of the rotators. Good luck!
Jerry
