Frank,
The Fox 29 is the same case, crank as the 35. The 35 has a thinner cylinder this makes it vulnerable to distortion. I think for the ships in the size range of the 35 that the 29 with the right prop will do as good as the 35 and be a bit more consistent. Don Still used the Fox 29 in the original Stuka and it did just fine.
Best, DennisT