There's a tech article somewhere about using 3 3/4" diameter Cadillac pistons and 292 rods in the 261 with a stroke increase by offset-grinding the crankshaft to the smaller-diameter 292 rod journal size. One option is to simply grind the center of the journal, leaving a partial shoulder on both sides for rod centering, while another option involves welding material onto the stroker shaft to give a narrower rod journal with a full-circle flange. Either way is expensive, but the resulting dyno numbers are pretty impressive.
Edit: There are several ways to identify 261's, but the most obvious difference is a set of parallel bars cast into the block near the starter, and a similar set of bars on the passenger's side near the oil pan rail about halfway back on the driver's side. They're often called "captain's bars" because they resemble the military rank markings. 261's were used in heavy trucks, school buses, and some "Pontiac" passenger cars in Canada in the late 50's and early 60's. Their major claim to fame is a 3 3/4" bore size, with the same stroke as a 235 engine. "There's no substitute for cubic inches"!
Jerry
