Good idea on the 2x6's.
Found the date code on the engine, J268. Translated it means the engine was cast on Oct 26 of the year ending in a 8.
I'm going to guess it's a 1978 as it appears Chevy stopped putting the 250 in USA vehicles in 1984.
It now appears the block was cast Oct 26 1978 and installed in a 1979 Chevy truck per all the good info y'all have provided (Gord, BC & Jerry), so I'm going to call it a 79 250 truck engine which should have a 2bbl intake hidden under that Q-Jet.
With that ciphered I moved on to the Q-Jet carb. The ID is: 7042210 QE2711 That translates out to a Federal standard 1972 Q-Jet with a divorced choke thermostat that came on truck 350ci engines.
On this engine theres no choke thermostat of any kind much less a divorced thermostat. They've got it rigged to be fully closed and use the choke vacuum pull off to fully open it once it starts. This might explain the loss of power when I opened the throttle and also why it wouldn't "kick down" to a lower rpm when I goosed it to get it off high idle.
Curiosity is killing me so once I can get back on it in a couple days I'm going to rig up a manual choke 1st then try it out. I'm also going to go through all the vacuum taps as I don't think they've got those connected correctly either. Basically go through all the easy stuff before going deep. If that doesn't get it going right I'm going to pull that Q-Jet, see how it's adapted and either marvel at it or laugh at it then determine the next course of action. I'd like to see if that engine can run good with that big mutha hanging on it LOL. Course I'm not adverse to putting the correct Vari-Jet 2bbl on it if all fails.
Engine casting numberEngine date and Con numberQ-Jet choke side picEngine serial number 
