There is a guy in vic called Phill Soderstrum.
He is the power glide king of australia. He can manualise any valve body you want. But if you manualise the valve body you will get harsh shifts. You will have to ring TCE there a torque convertor company & ask them how to get on to him. 03 9879 8455. they send converetors all over australia so a valve body wont be a drama. You DONT have to pull the auto out to do the job but to do it properly you should reco the trans aswell. I think you will get more out of a manual gear box & more fun and cheaper. But theres nothing wrong with being differant. good luck if you have any dramas PM me
P.S I think phills a bit of a grump as he probably should be retired but drag racers wont let him. He is the best in the buisness.