Sealing the pipes in the head.
ordinary silicon bath sealer works, black stuff is less obvious, all mating parts should be cleaned to bare metal, , degreased , then given a final rub with vinegar and wipe dry with a towel before applying the goo ( acetic acid is the solvent in most Silicon sealers).
if all is clean it fills pretty grim amounts of wear, my 71 head is wallowed out and it works on that.
use a bit more vinegar to clean up excess squeeze out. It does not burn or melt. If you can be bothered some dangerously sharp beer can shims will help , I always cut myself on these and have since given them up, but they do seem to stick in very well when siliconed and shimmed.
Fitting pipes with a balancer , test fit , make sure everything lines up and you can slip the balancer around before getting goo anywhere,, push the balancer all the way to one side. Smear goo in the ports, a generous layer with a gloved finger, offer up the pipes and jiggle into place entering , shifting the balancer , repeat a bit at a time, wipe up the goo,
, slip the balancer around getting goo into the slip joint and tighten the clamps, after a heat cycle re tighten.
I sometimes use Exhaust putty for the balancer pipe, it comes apart pretty easily..
Theres at least two types of balancer clamps out there, some have tabs welded to the balancer , others have two splits and need two separate clamps, the clamps tends to bend and settle and need a retighten every now and again.
One other thing, According to the Umberslade hall book the exhaust port angles changed subtly for the OIF models, I had never noticed, but if your head is unworn it might make a difference when fitting earlier types. And might explain why the siamese set up was reluctant to stay in place when I tried it.