For sake of clarity, Jim explained that he was planning on running the engine on a muffler, not using a pipe, and in that case, I would suggest that the 67LS or 76 might be a better choice, given the low revs. The 61 BSE (at least the 136 ad 140 degree versions) run OK on a muffler, but you definitely give up performance at the lower revs.
Any of these engines have *plenty* of power for most current airplanes that were originally designed around piped 40s, it's how it is delivered and how it affects the trim/cornering is the trade-off.
Brett
p.s. the real issue is controlling the excess power without any regulation, of course, and that is what has more-or-less prevented widespread use of super-large engines even though they are now perfectly legal (unlike the old FAI limit of .61 cubic inches) - the bigger and more powerful the engine the more you need some sort of regulation (i.e. a pipe). This certainly brought Windy to grief, but he is not alone. The issue is as described at length before - these huge engines are so powerful that even if you can control them to within, say, +-5% of a constant output, 5% of a 76 or 88 is a lot more absolute power change than 5% of a 40.