th400 fixed yoke or slip yoke?

[Greasey Harley]

I'm getting read to swap my '68 c10 to an automatic transmission.
The transmission builder wants to know if I want a slip yoke or fixed yoke on the th400 he's building for me.

keep the 2 piece driveline or install a 1 piece
it'a a short bed, how were they setup from the factory?
should I keep the 2 piece or convert it to 1 piece?
fixed yoke or slip yoke?

My thought is; install the fixed yoke and use the existing 2 piece drive shaft,
it's already there and is in good condition.
Just shorten the front shaft.
is this the best route?
The truck is static dropped 3.5/5, the current setup works well. it's just a cruiser, but hauls the occasional motorcycle or load of mulch, if that matters