Did you use a timing light when you set your ignition?
Use a timing light to see what your initial advance and total advance are. if your engine barely turns over when you try to start it, that is very indicitive of having the initial advance set too far forward.
Try resetting your distributor at about 10 degrees of initial advance and see if you still have that problem. If you do, as far as the backfiring, it sounds like carburetor or possibly valve set too tight.
A quick way to check it out is to just loosen the distributor a bit and slowly retard it while it runs. If you are way too far in advance, you will notice a slight pickup in rpm, as you retard it.
But, to properly set it, you need a timing light.