Here's a modification that just about any machine shop can accomplish on a 235, with modern parts and a crankshaft that might be considered "junk" for a conventional rebuild. A big block Chevy V8 runs a connecting rod bearing that measures 2.200", considerably smaller than the 2.312" stovebolt rod bearing. Those "worn out" 235/261 crankshafts that have been reground .030" undersize and worn out again can be reground to use a big block V8 connecting rod and bearing, and there's a custom length BBC rod that's 7.1" long. That rod, and a crankshaft that's had the stroke changed to 4" instead of the original 3 15/16", plus a set of 92MM pistons for a Japanese diesel engine can be massaged together to get 247 cubic inches, a pretty good compression increase, and the engine still looks completely original from the outside. "None of the above" is a drop-in fit, but it's pretty much routine work for anybody with the unmitigated gall to call himself a "machinist"! Another option instead of the diesel piston for the same setup would be from a 223 cubic inch Ford inline six, produced from 1952 to 62. Both pistons are approximately 3 5/8" bore, and they're almost exactly the right compression height to work with the above rod/stroke combination with just a little bit of tinkering on the wrist pin diameter and compression height.
There's also a 96MM diesel piston with the same design that will work on a 261 stovebolt. With a 4" stroke, that one gets 269 cubic inches. Pistons for a 265 Chevy small block V8 will also work with that rod/stroke combination on a 261. With a 4.25" stroke, a flathead Ford V8 connecting rod, and a .060" oversize 265 Chevy piston, the 261 gets all the way to 291 cubic inches!
Jerry
