Personally I tighten the head end first, then
'adjust' the frame bracket to suit. By doing it this way, there is no stress put on the head, the exhaust or the bracket and hopefully no cracking of anything...
I have also found it good practice to fit either a longer stud or a longer than required bolt that bottoms out in the head hole, with TWO locking nuts
(put the locking nuts on the bolt first before fitting to the head) then tighten the first nut down so every thing is tight, while holding the first one still with one spanner, thighten the second nut with another spanner to lock very thing in place....job done.
Using this method
(for many years) I find my nuts do not come loose in my head!
and every thing stays where it should be.. ooo er misses
.