It wouldn't run if the timing was off 180 degrees, but all you symptoms
point to the same problem.  The cat was glowing because it was being
asked to burn so much fuel.  The backfire that blew the muffler apart
was because there was unburned fuel in the exhaust that was ignited.
The exhaust smell like gas because, well, there's unburned fuel in
there.  

Unfortunately you've made so many changes at once, fault tracing could
be difficult.

1.  Check your injectors, if you have the wrong ones, the thing will
never run right.  (Put in you old ones if you still have them.)  Or
maybe you have the wrong fuel computer - one designed for different
injectors.
2.  Check ignition timing - it sounds like it could be way retarded.