I'm working on a parts list that will turn a 261 into a 291 cubic inch displacement engine, using a stroker crankshaft, some creative machining, and pistons for a Japanese Diesel engine. 4 5/16" stroke, a 96MM bore, plus flanged slip-fit cylinder sleeves which will eliminate the need to rebore the block on future rebuilds. It takes about 15 minutes with a Dremel tool to make the newer design main bearings fit an early block.
Jerry