I replaced main relay and starter and spark plugs and about to change distributor when it arrives but it just doesn’t crank at all and oil light comes on and fuel still primes but nothing what can I do? Any help would be much appreciated.

 

Sounds like the starter solenoid isn't getting activated. Check the small wire that connects to the starter via a spade terminal (not the main power wire from the battery). Make sure it is plugged in. Make sure it gets voltage when you turn the key to start.

Also, make sure your all your engine grounds are attached properly.

Lastly, make sure your battery voltage is > 10VDC.