I just did this a few weeks ago and I wanna say about 70 ft-lb?

Edit: checking ARRC, the spec for the flange bolts (is that what you want?) is 70-95 ft-lb.

 

85-90 pounds or tight as ####.

put a 12 box wrench on it, and use your foot to tighten it

 

«1992 Mustang Service Manual Table of Contents»
«Group 05: DRIVELINE»
«Section 05-01: Driveshaft»


SPECIFICATIONS TORQUE SPECIFICATIONS

Description---- N-m ------ Lb-Ft

Flange Bolts--- 95-130 ---- 71-95

 

and keep that wrench in the car.