SeaSloth - If I understand you correctly you're replacing some PVC elbow
tail pieces with Groco elbow
There have been many excellent responses, but here's another response to consider.
1. Over torquing can cause galling of the metal fitting materials, not to mention cracking them. Plastics will just expand or crack.
2. It is best to use non-hardening pipe paste with metal NPT fittings. The issue is the sharp metal threads can cut the tape. Although given the low water
pressures the vast majority of below the waterline fittings will encounter (5 psi at most) this should not be much of an issue, but I'd still go with the paste with either metal or plastic.
2. The ASTM standard for NPT threads is 4.83 threads hand-tight to closure. I.E. all the thread surfaces locking. However, that's the ideal, I've tested NPT marine
fittings and, hand-tight they range from 8 turns and still loose (Shields barbed fittings) and 2 turns to hand tight (West Marine
white nylon fittings). Even the high quality threaded hose fittings I had molded were + or - 10% of that number, but at 5 turns with just a few wraps of tape would hold 50 psi.
3. THE GROCO tailpiece is well made and should be close to the 4.83 turn number hand tight.
4. I'd use non-hardening pipe seal and hand tighten the elbow, then go 3/4 to 1 or so turns more to position the elbow to where it fits best. Unless the fitting is improperly machined, which I doubt, you'll be leak free.