Slip yoke on a TH400

[leddzepp]

I am at the point of putting in a driveshaft on my SWB project truck, and was wondering how much "slip" is needed on a TH400 mated to a 402? I have a factory 2 piece driveshaft from a SWB parts chassis that I mocked up (This is the correct TH400 yoke). I measured and there is 1 3/4" before the yoke bottoms out on the tailshaft housing. Here is a pic to illustrate. Yep, I plan on replacing the u-joints too Thank you in advance.