I'm re-writing some this because of corrections in the math due to finding the actual right angle ratio.
Just use the motor trans and front diff from an awd astro van.
What you may not have noticed is my plans for 50-60mpg. I love my diesel because of that and it's torquey, which I'm aware isn't really required for these cars but is a lot of fun. The diesel will also be a breeze to get running because it's mechanically injected and require no computer, I'll post a pic of the engine wiring later since I just wrapped it. I also already have the engine and trans, which saves me times and maybe money depending of the price of syncro diffs. I do realize that this will provably be as expensive or more so than a normal low cost, my saving grace will be having the engine and trans, which are worth at least $2k for what I'm running. The parts I'll be needing for drive shafts are cheap too so that will help too.
To get the speedo to read correctly, I need to either change the gear or adjust with tires. I decided (after finding correct info) to do both. If I use the speedo gear for the gas trans with the 3.667:1 diff I get a speed rating 5% too high, the trans is spinning faster than it normally would for the same speed. The rest is just tires.
I did a little work with this last night: tire calculator
. Stock the golf comes with 175/70-13 tires, which have a circumference of 71.1 inches, I found 205/55-15 has a circumference of 75.0 inches, which would make my speedo read 5.4% slow according to the calculator. That's exactly what I want however because the diff ratio of 3.850:1 is 5% lower than the stock 3.667. So with 205/55-15 tires or an equivalent circumference both the speedo and odometer would be correct. I'm thinking I could check that with all the radar signs in my area
. I'll probably get some 205/55-15 Michelin Pilot Exalto A/S tires for regular driving, and some 225/50-15s slicks for funsies
Also here's a quick sketch I made (in paint) of the drivetrain layout:
The colors are as follows:
Brown: Engine, intake and exhaust are on diver's side
Grey: Transmission and diffs, the front diff is being turned correctly the rear is reversed
Orange: Axles, regular fwd VW axles bolt right up to these