Re: "I was building a nice 650 cc WL/R [WL cases machined to WR specs] motor before the rule change. I think it would have been competitive with hot 350 cc OHV bikes."
I had the same thought, never went any farther due to being near the end of the "to do" list.
The existing record (as of August 2002) was 89.834 mph, held by Dale Martin on a Triumph 350. I was going to shorten the stroke:
Engine displacement for class is allowed to deduct .050" of bore size:
2.745” std. + .050” overbore - .050” allowed for class = 2.745” × 3-5/16” stroke = 39.36"or 643cc (the actual displacement is 40.65" or 666cc). I didn't go any smaller (sleeved down to 2.59" × 3.00" stroke is 498cc; ran against 250 OHV under the old rules, against 350 under current rules) because Truett can't move the pin down any more, and because getting compression with a smaller engine will be really tough.
The shorter stroke gives about the same inertial load (107,000 f/s/s max accel) at 7,600 as the original stroke does at 7,000. The rod ratio also goes up, which should help the small intake ports.
As a guess, 35 hp looks good.
I could still build the engine, but I don't have a suitable chassis...