Another thought since there's a lot of discussion about weight. My PT-60 built very tail heavy. With the TT-61 it needed about 3 ounces of added nose weight to balance.

The TT 61 is listed on Tower's site at 26.1 ounces with muffler
OS 70 Surpass, 22.1 ounces with muffler
OS 91 Surpass, 24.2 ounces with muffler
Horizon's numbers are:
Saito 82, 17.6 ounces with muffler
Saito 91, 21.0 ounces with muffler

So, in my case, a lighter engine would have just meant more lead on the nose.