Good points by 1320feet. I will add, the +.100 longer valve is adding to the issue as the tip is now closer to the stud center-line. Also, although a great video on the "Mid lift theory" and attaining it's geometry, it's a BBC, your working on a SBC, with a stud mount arrangement, and this generally favors the "low pivot" option. Crower do make .090 backset trunion RR for this setup. I think they are not cheap at $380 for a set of 8. So get out your wallet on that one for sure. The last thing I buy is the push rods as you do not know what length you need until it's all assembled. And use your real springs for final checks and patterns.