I am looking for whatever cylinder head works best (in terms of responsiveness to tuning) with a 3.090 (75.7mm) bore cylinder. A 650 head works with the 750 kits but it is not optimal. The last 9-bolt 650 heads, the ones with the bolt-on intake manifolds and the boss for the tenth bolt, have better port profiles and flow better than the earlier heads, as do T140 10 bolt heads. I also like the rocker box arrangement on T140 heads better. However, I'm not interested in re-engineering the top end just to make a 10 bolt head work.
I was hoping someone either (1) has seen it done and knows the answer or (2) has both a 9 bolt and a 10 bolt head on the shelf and could bolt them up with the cylinder faces together and compare the center bolt holes for me.