Trouble adjusting dizy when hot

Loosen the dissy cold and check how much f tor and l to r movement you have. As the dissy on a small or big block chev is located by both the block and intake manifold it may be getting jammed as they expand on different planes. If one side has a higher deck/thicker head it will sit the intake on an angle. The dissy should be centred in the top hole cold and you may have to move or machine the intake to achieve this. I've seen a 350 Chev with a dissy that would lock up and retard the timing if it got too hot, the intake got machined to cover up an obvious deck height issue ( Dandenong Vic engine shop in the early 80s)