Cold Engine Stall Until Truck Moves

[Butalla]

I have a really bizarre problem with my '86 C10 that has me stumped.  When it's below about 50 degrees and the engine is cold, the truck starts, but is weak and dies rather quickly.  If I start it again, it's the same problem.  If I press on the accelerator, it will stay running until I let off the gas.  Now here's where it gets strange.  If I can get the truck into gear and move forward, it will still die, but the next time I start it, it's fine.  I can start it over and over and it continues to stall until I can get it to move forward.  I don't even touch the gas pedal. 

I thought it was related to the vacuum line going to the TH350 trans, but this summer I installed a 700R4, and now that it's getting cold, the problem is back.  With no vacuum line to the transmission, it's obviously not that.

I first tried adjusting the choke, but it seems to be in the ideal spot, plus as I said, I don't have to touch the gas pedal after the initial start.

I have a bit of a franken-engine.  The original 305 engine had all the electronics removed.  The right cylinder head is from a 1971 Monte Carlo 350.  It has an Edlebrock intake manifold.  The carburetor is a Rochester from a 1979 Malibu.

I'm out of ideas, so any thoughts are appreciated.

[Irish_Alley]

so one head is a 350 the other is a 305?

[Butalla]

One head is definitely from the 350.  The other I believe is original which according to the VIN is a 305 though I have not verified that head by the VIN.  I just know it has the stock style exhaust manifold on that side.

[Irish_Alley]

stock style? whats on the 350 side?

[Butalla]

It had the stock style exhaust manifold when I bought the truck, but there was a leak.  Turns out the last bolt was missing because the hole didn't line up.  Found out the head number was from a '71 Monte Carlo.  I had to buy a different exhaust manifold to fit.  That one goes under the plugs.