To the OP, if I were you, I might leave the TH400 in there, change the gears and see how you feel about it then. Take 1 step at a time until you have it exactly how you want it. Many rodders try to take too many steps and either end up spending a fortune or losing interest with their project before it's finished. I know I'm guilty of it and I'm sure many of the guys on here are too.