I'll settle for part of one

and already have the red brake calipers

Have pondered the possibility of V8 gearbox internals in my Roadster though.
3.7 V6 v 5.0 V8
First 4.236 3.657
Second 2.538 2.430
Third. 1.665 1.686
Fourth 1.2387 1.315
Fifth. 1.00 1.00
Sixth 0.704 0.651
Richard that sounds an interesting swap, you have the gearbox ratio/engine mismatch sorted then I guess, is it a straight swap or literally internals?
Don't know if it's possible John as cannot find on the net anyone that's bothered to do it. Cannot see why not though assuming casing is the same. It would provide a more usable first gear (even MMC suggest starting in second) and the same fifth gear ratio. Sixth would be a little higher still but have to change down at present to overtake efficiently on motorways so no further hardship and possibility of marginally better mpg.
It's sounding like you maybe the one to break the water first Richard, it sounds far more usable from your explanation.
Presumably this ratio mismatch comes about with the differing weights of Mustang to Roadster as John seemed happy enough with his Mustang in USA last year.