I removed, cleaned and replaced the stock exhaustmanifolds and some of the old metal tab nut lockers broke or are missing. Not sure I need them. All factory going back on.

 

Lock washers will loose tension due to the heat. I'd go with lock plates.

 

Put a little anti-seize on the threads if you ever want those bolts to come out in one piece again.

 

You can make your own lock plates with some sheet metal and tin snips

 

Nah, GM just put them on there for sport. <heavy sarcasm> GM used them because they didn't want warranty claims and service calls for leaky exhausts. If you want them to be leak free and can't afford for the bolts to work loose, a similar locking solution is a good idea. I seem to remember seeing the factory style lock tabs in the Help! section, but I haven't looked in years. Plenty of older GM applications have reproductions available, one of them might fit. Or get super trick and safety wire all your hardware for that aircraft look. Or just let er buck, because you can always torque the bolts again, or deal with the problem when it presents itself.

 

I have had my stock L69 manifolds installed now for a few months. The mechanic did not reuse or add any locking tabs and did use the high temp anti seize on the bolts. After a few heat cycles I retightened the bolts, on a cold engine, and a couple were lose. I have had none loosen up since and I just checked them a couple weeks ago.