building a cobra from basically scratch

[thefordguy]

there are actually 6 cross members, And 8 gussets, and the entire frame is 1/4" steel. I don't claim to be an expert frame builder but for a 302 I think It's a bit over built. If I jack it up on one corner and it teeter totters between the jack and the one remaining wheel on the ground with out flexing I would say It's pretty stiff. But, correct me if I'm wrong I'll build it better. I've never built a frame or a cobra before so any input/suggestions are appreciated, just don't be a dick about it. But anyway, I got it running today, fired right up on the first try. It sounds pretty mean, and no exhaust leaks from the headers I built thank god. 50 psi of oil pressure at idle! I made a movie of it cranking up but I can't seem to get it from my phone to the computer Any weber carb gurus here? when I bring it off idle it makes a little backfire out of the carbs which would suggest it's too lean, but when I rev it up and let off it backfires out of the exhaust which would suggest rich. or a timing issue. I have static timing set at 10 degrees advanced, and I moved it from 5 degrees to 20 degrees advanced and I still get the same backfires so I'm assuming it's in the carbs? I've never fooled with webers, I'm a holley guy. any tips are appreciated. also it does the same thing weather I open either carb or both. thanks