Engine Issues, Popping Through Intake

Hi guys, I've been a lurker on the site for a while and am finally fed up with my fox enough to make a post.

I recently did an engine and tranny swap in my mustang. It was 5.0/auto and I switched to a 5.0/t-5. On the new engine I installed gt40p heads, and explorer intake/plenum. I didn't do any work to the heads or intake(other than what was necessary to get the lower to work), the block and components are stock.

I started the engine for the first time and had loud lifter noise and popping through the intake at idle. Replaced the pushrods (they were 4 different lengths for some reason) with stock 6.250 length and that fixed the lifter noise. It now only pops through the intake while trying to accelerate and only under 2500 rpm. As soon as I get above 2500 it runs fine, no popping. The engine runs very rich. I have checked my TPS, IAC, and MAF and they are ok. The EGR was deleted by previous owner.

Changed plug wires, and distributor cap (I had an extra set) no change. My plugs are Autolight 764s and are new.

Is there anything else I should check on my motor and what is causing my popping?

Thanks.

EDIT - it's an 1989 Mustang Lx

Nevermind, just saw a guy had posted about this similar issue just a few days ago. Mods can delete this post.