Sb350/th400/np205 drivetrain set up

[Furno68C20]

Hey guys and gals. I’ve got a 1975 k20 that originally had sb350/th350/np203 set up from the factory. I’m swapping to a th400 and np205. The 400 is a little longer in length by a few inches, which has basically moved the driveline back. My question is what length rear shaft would be the correct fit to accommodate this extra length, or do I use a 60”shaft with a shorter yoke?

Also the front shaft has also extended to accommodate the th400. How much can the front shaft telescope without having any drive issues?

Thanks!
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[kwmech]

You've also got to factor that the 203 is longer than the 205. Either way, put it all together then get a tape measure and take the drivelines to a shop that can shorten, retube, rebuild and balance