I'm using a m2j5 witch is the f22B tranny. A Lil shorter than f22 but longer than h23 tranny. I think the h23 trannys Max out at 150. Shorter gears do make accelerating faster in some cases. Like all motors where u need all the help possible. I like the longer gears ratios personaly. Tq will propel your long gears. Almost like a slingshot if your Gonna be around the 400whp go with h22 tranny. If your going higher your gonna break trannys trust me. But then you could swap out gears cus by then you would know witch gear is lagging or is too short. Ive never heard of people having issues with that head swap??? Its just a bolt on everything matches except the 87mm CC Nd the 85mm bore on your block. But by the time you bore to 86mm BISIMOTO turbo pistons it won't be lot of difference. So if you don't go with h23 head your going f22a6 head? Oh Nd BISIMOTO gots the headgaskets in custom sizes so you won't have a problem their