New to all this, fighting my new carb on my c10

[JTknives]

Well I'm a brand new member, but I have read a lot of posts from here in my quest to understand what my problem might be. I am looking for advice on what to do next.

First off I just got a 1970 c10. The engine in it is not original, the guy I got it from said it was swapped out. I don't know when it was done. The casting number says it's from a 1971 caprice with a 2 barrel carb. But it had a 4 barrel quadajet on it. And the casting numbers on the heads say thy are from a 305. So I got a bastard engine.

When I got it I replaced everything as the carb was not working right. I got a brand new eddlebrok 1406 4 barrel. and all new ignition. It runs good but has so lag from idle. But my big question is this. I'm at about 5,000 ft elevation and I'm wondering if the carb is running to rich. The exhaust is VERY stinky and burns my eyes. If I walk past the tail pipe while it's running I will stink all day. Also I ran a compression test and I'm at 120psi and according to my math with a compression ratio of around 9:1 and at 5000 ft elevation I'm in the ball park being that my atmosphere pressure is only around 12.3 psi up here. I'm about 16-17" of vac. But what got me concerned was when I put some gas in it and did the math and was only getting 7mpg. I know I should not get great MPG but 7 seams a bit low. I do have what looks like a little carbon on the plugs. But I don't drive it a bunch. About 3-4 miles a day.

I picked up a eddlebrock carb tuning kit as there manual says I need to be about 8% lean at my elevation. But I'm clueless as I kinda got a bastard engine. But I did pass emissions at something like 135-150 hydrocarbons and our limit here in Utah is like 500 I think. My carbon monoxide was around 3% and out limit is 5% I think.

So any help would be very helpful. Thank you so much guys - JT