I looked in my 1976 Ford shop manual and there are no torque limits specified for the intake manifold. It is listed, right next to Exhaust, but it is blank. Further down the page there is a table for "Torque Limits for Various size Bolts-FT. LBS. The bolts are 9/16 heads and the shaft is about 5/16 best I can figure. The value for 5/16-18 bolts is 12-18 FT. LBS., does this sound right? I would think it would be more, but when I took the intake off the bolts didn't seem to be very tight at all, so maybe this is right.
Three of the four corner studs came out with the nut, so I cleaned them up, checked the threads and put the studs back in with red Locktite. One of the bolts was actually a stud with a nut on it, and one of the other bolts was of the wrong type. Tomorrow I will see if I can find two replacement bolts and then hopefully I'll be able to wrestle the intake back on tomorrow evening.