Timing Marks ?

[twoskies]

hello

1972 c10 with a 1979 350/4 motor

had some issues recently with running, ended up being something i changed, changed back, now it runs, seems ok

Here's the question

TDC set by holding finger over number 1 plug hole, then turning crank to 0 on timing tabs

set distributor in rotor to number 1 plug firing pretty much pointing at number 1

starts up ok,
Timing marks never show with timing light, have to set by ear

as stated, seems to run ok, but bothers me that marks dont show

any help appreciated