The 261 can be built to 300 cubic inches with 96MM pistons and replaceable flanged sleeves for a Yanmar diesel, a 4 3/8" stroker crankshaft, and H beam rods for a big block Chevy V8. Use the 848 head with the big valves that Mike suggested, (about 9.5:1 compression with flat top pistons) and machine the back of the block for a full circle lip oil seal. The big problem with that buildup will be finding a machinist who knows what he's doing to make it happen.

Mike, the lip seal conversion is simple- - - -use a portable boring bar mounted to a plate bolted to the back of the block, center up in the main bearing bore, and start whittling. I made my own mounting fixture from a piece of 3/4" thick steel plate. The seal I use takes a 4 3/4" counterbore 3/8" deep. The seal part number is a Timken 417210 or equivalent. The seal lip has enough flexibility to handle a 3 7/8" stainless steel Speedy Sleeve on the crankshaft. That same seal also works on a 216 and a 235- - - -same setup.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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