Rear end and transmission

[profe56]

I need to start buying the necessay parts to convert an 73-87 rear end in coils instead of leaf for my C10 69, but also in the future I´d like to do manual to automatic conversion, TEXAS FIREFIGHTER gave an excellent guide to do the rearend conversion and I was thinking if taking the parts from a truck that has a 700r4 transmission and the rearend could be a good idea or should I look for the best ratio not just any rear end?

[piecesparts]

My suggestion is to look for a gear ratio that would give you the best fuel mileage and also the right optimization of your engine's torque. You will need to calculate your tire size, gear ratio, and the fact that the tranny has a .68 output ratio.

My 84 truck has a 700 R4 tranny with a 28" tire and a 3.73 rear end ratio, this gives me a solid 2500 RPM around 75 MPH and that works well with my cammed up 383 stroker motor. My daily driver 91 Silverado has a 28" tire, 700R4 tranny, and a3.42 rear end ratio and it runs about 2200 RPM at 75 MPH. These ratios work well with the types of fiel management systems that I am using.

I would shoot for an RPM that would put you in your best area for your engine's power curve.