Re: Manual conversion - Toploader or T5?
What Ben says is very true,
but, you must ask some questions.
Your final drive....are you hitting peak revs long before the end of your straight?
if so you need another gear!
Don't forget in either Toplader or T5 you can have wide or close ratio boxes.
Both units will bolt up to and ford item without modification, so depending on your final drive, you may need both to suit different tracks.
One of my customers, has a pretty wild 69 Mach1 Mustang, and he has 7 sets of rear gears and runs only one box (a 6 speed double overdrive Tremec).
You have to to decide if you want a universal box, or be prepared to swap boxes or diff gears to be competitive.
If you have no interest in being competitive, and only wish to thrash it, the forget all i have said, go toploader and your current final drive, and be happy trading paint at the back.