Drivetrain Custom Shaft Measurement

I've been on the phone with the guys that are going to build my driveshaft and they're wanting some information (obviously).
They're looking for a center of cap to center of cap measurement for the shaft.
Obviously that requires I already have the trans slip yoke and a pinion yoke. I currently DO NOT have a yoke for the TH400. Need a recommendation there.
I also don't know what U-joints to go with or how complicated that may be to answer (I'm assuming not very).

Driveshaft will be steel. Through a 400 it will see 8,000 max RPM

I need to get a trans yoke so I can get these measurements and hopefully have a shaft in the car next week.

@84Ttop @srtthis @anyoneelsesmarterthanme

I've got a stock pinion yoke in it now (1330 joint?) and was going to just run a steel slip up front (looks like th400s only have an option of a 1310 or 1350) so a 1350 up front.
I'm not making gobs of power but a tbrake is gonna break whatever it can find so would you think I need to spring for a forged transmission yoke and go 1350 rear?