Alright guys, got an update for all those that helped me with this thread. After a lot of thinking and troubleshooting I decided to throw a new distributor cap and rotor on it today to completely rule out the spark "crossfiring" possibility. I also bought a new fuel filter and replaced that today as well. After changing those things I hit the key and.......... same old thing, no start. I proceeded to crank and crank until the battery died then got out the jumpers. When replacing the fuel filter I captured some of the gas and to get a glimpse of the condition of it. Well the gas was very brown, likely from rust formation inside of the steel gas tank, especially since the truck had been sitting for over 3 months. I then figured that the gas in the lines and rest of the fuel system may be so bad that it is the cause of these problems. To further rule out the ignition system (which is basically all new now) I poured some gas straight into each of the 6 intake runners and then hit the starter. Well sure enough the engine span up to 5000rpm on its own for a mere 2 seconds then shut down. This further supported the idea of poor fuel in the system. I continued to turn over the engine in hopes of clearing all the old fuel from the fuel system, a lot of it had already been removed when replacing the filter. Sure enough after much cranking, she fired up!!
It finally ran and wasn't misfiring NOR backfiring out the intake anymore! Success!!
So, with this in mind it appears the root of the cause of this problem was simply old/rusted gasoline.
The fuel pressure regulator was leaking and did need replacing ofcourse but really all I had to do was evacuate the system of all the poor fuel and it would have eventually ran proper! In the meantime I've spent sooooo much time replacing ignition components and troubleshooting a multitude of things. It still baffles me WHY the engine was shooting flames out of the intake all due to poor gasoline? It is no longer backfiring meaning the gas in the fuel system now is much better. I just can't seem to understand how poor gas could cause backfiring out of the intake, its not like the timing has changed or anything. Anyhow, I am thankful I finally figured it out and thankful to those on this board who chimed in. I hope my findings can help somebody in the future if they encounter a similar problem, step one....... CHANGE THE FUEL!
P.S.- If anybody would like to explain to me WHY poor gasoline was creating this backfiring condition, I am all ears.