Most of the 350 and 400 fours will no longer "self adjust" because the tension springs have lost strength - they've been sitting compressed for decades. Usually they need a bit of help, lots of descriptions here but essentially you remove the cap bolt above the tensioner lock bolt and push down inside from above with something thin, a longish 1/8" blade flat screwdriver works or use a nail. Follow the manual instructions, but press down with increasing pressure until the chain rattle JUST disappears, then tighten the clamp bolt (not too tight, they love to break off) and its lock nut. Done. Over tensioning past where it quiets will cause increased friction and rapid wear of the tensioner blades. Replace the cap bolt
The springs etc are captive and don't come out of the cap bolt hole. No oil will squirt out. No drama at all, just a quiet engine afterwards.
This risks severe hand and arm burns from the very hot headers: be super careful!
