95 Yukon 5.7 tbi no start... help me see what i'm missing!

ok, hope this isn't that long but here we go.... Engine ran great but never got up to temp in the 6 months I've owned it./ Replaced both temp sensors replaced thermostat with a new one and then a known good used one. Would only get up to 185-190. Installed an aftermarket gauge to confirm. The engine was badly rusted, to the point that when i tried to pull a plug to do a tune up the plug snapped, leaving the threads in the head. I was able to extract the rest of the plug but every plug i tried to change snapped. I pulled the truck into the garage and decided it was time to replace the rusted headers so i would have more room to reach the plugs when they snap. removed headers and all plugs, snapping 6 of the 8. Got everything removed and installed all new ac delco plugs, gapped to 40. Put on new headers, new valve covers, new idler pulleys, new belt, new ac compressor, ac condenser, all new ac hoses and a new belt along with a new cap, rotor and wires Now the truck wont start. it cranks and i get the occasional pop but no start. there is occasional fire coming out of the header collector but its more like fire coming off a torch or a big ass candle, not fire being shot under compression. I also get the occasional backfire fire ball coming out of the spider injector area. the truck never had a no start issue before. I didn't touch the timing but i also noticed that the old wires were not in the correct firing order, unfortunately my son took them off the cap before i could return with my phone to take a pic, so ill never know how the guy had it setup. I've loosened the dizzy and set it up with #1 at TDC but nothing. I had my son crank while i turned the dizzy in both directions and it still never tried to start. i have fuel, i have spark and air...what am i missing? I removed and cleaned the ground but that didn't help. it has to be something stupid that I'm missing. Thank you for any help!

Pull the cap, watch rotor, ground coil, crank engine get #1 on compression, where is rotor pointing? No.1 on cap ? Recheck wires in correct firing order. A 95 is a TBI with two injectors, there is no spiders. Do you have the OE service manuals ?

Confirm that you actually have spark and fuel. If you do then timing of the spark is the most likely cause. If the plug wires were previously offset to compensate for the distributor being out of position you could easily be farther off on timing than moving it both directions would solve.

Sorry it took awhile to reply, my mother is in the hospital and it's been a **** show. You guys were 100% correct! I went through the steps to set the timing from the beginning and the guy before either stabbed the dizzy in wrong or it jumped timing because at TDC the rotor is facing dead center of the firewall, straight back. For now I just made that #1 and it started right up and runs great once again. Thank y'all, I knew it was something simple but I was over thinking everything and forgot to go back from the start. Than you again!!!