Master Cylinder / Brake question

Just had a local mechanic do a disc brake conversion on my 1966 Lemans.  Having
two issues that he can't figure out.  First no pedal on first pedal pump.  After you pump
it the second time, you have pedal and it is a good pedal with no fading.  Now talking
to the mechanic he said the old pushrod from the single reservoir wouldn't fit so as I
said yesterday he got one locally but said he had to leave the bullet or slug (piston
adaptor that came with the new master cylinder) which states to keep it in the back of
the master for power application and remove for manual application.  I have manual
brakes.  Since it is holding nice with no fade after the first pedal pump, my thinking is
that the pushrod he used is too short and not going in far enough to make enough
pressure on the pedal press.  I think I need to buy an adjustable universal gm pushrod
but I don't know what the travel is for the master cylinder I bought online.  I don't want
it to go too far because that will build up too much pressure.  Any ideas??