Not sure on all these questions, thats why I'm posting about it. As far as your rpms there 428, thats ridiculously high! I have an 83 grand marquise with 25" tires, an overdrive transmission, and ??? rear end gears and doing 70 im only at about 1750 rpms. Not sure what the gearing ratio on it is in the rear but she accelerates pretty well.

I think switching over to the overdrive would really help you alot. If you do your engine right you could still retain monstrous acceleration too.

Wish I could post pics ofthe kit and all but im in Iraq still. Go to google and search patc aod transmissions, they will have conversion stuff somewhere on the website