went to the local mud bog last weekend and two of the best running trucks had respectively 577 cu in and 557 cu in Ford power. I believe I have seen 557 stroker motors for sale but 577 must be pushing it pretty far.

Anyone got a guestimate for bore & stroke?

 

No need to guess:

Scat Ford Stroker Kits 460 to 557 from RPM Machines.

4.50 seems to be the stroke limit, so the 577 might have been an aftermarket block with a bigger bore.

Not sure on the max stroke, but these have been out there for quite a while.

Flatlander Racing - Ford Stroker Kits