Whats the best 5 speed to use?

[lts70]

I have a NV3500 in my 70 swb 2 wheel drive. It seems to be a good tranny to me. I pulled mine out of a 92 1500 Chevy with a v6 along with it's slave set up. I don't get to use the overdrive very often because of my 3.08 gears in the back and I don't have a speedometer because it is electronic.

I have a couple questions for you guys.

1) Is it possible to put a speedo gear in place of the electronic pulse so I can have the speedometer going again?

2) What would be a better rear end gear ratio for my overdrive and better lower end grunt?

3) I have access to a NV4500 for $400, Would it be a better tranny for my lowered 2 wheel drive daily driver than the NV3500 (just seems more popular with the 4X4 crowd)? Would it fit in place of my NV3500 without having to change my spline or drive shaft length again?

Thanks Guys