I've got a 1972 Mach1 with the factory 351ci in it.

When I go to start it (from cold) it will crank fine but won't fire. This goes on for a few tries and then it will feel like it's going to catch but won't. Then it will catch briefly, then catch and run for a few seconds before dying. A few more tries later and it will run. This process will usually take around 5-10min depending on how long the cars been sitting. It will even happen if I drive the car in the morning and then leave it all day, but not as bad.

It's got a mild aftermarket Roller Cam, good battery & starter motor.

Does it not have a choke?

I'm gonna say timing might be off.

electronic or points ignition?

It doesn't have a choke and it's got Electronic Ignition.