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
If I were building a true hotrod that I wanted to keep the 6 in I'd definitely go the 261 route. My machinist friend does have all the equipment like the portable boreing machine. I have other priorities for my funds right now for parts, but who knows. Maybe I'll build it that way to sell it. I don't know what the market looks like.
The 235 is an over the counter the PO bought so I believe that means it's a 59+ motor. The date code is I185. If it truly is a counter motor It seems like that should be 1965, but if it's actually a replacement block it could be 55. Seems more likely. The 848 head is H246. I started assessing it last night. Unfortunately it was stored on its side in a garage since 1977 so it was pretty stiff trying to turn it over. A little PB Blaster and Marvel Mystery Oil in the cylinders helped get thing moving again. I haven't pulled the head or oil pan, but I'll assume I'm going to throw bearings, rings and a head job in it at a minimum.
