I just replaced my 1406 on my '76 K10 350 with a SMI Qjet. Best decision! Cheaper than EFI and less headache; (since your rig is already setup for a carb). The guys at SMI were great to work with. I highly recommend them. I bought my Qjet from them right before going to Moab this past August. I tuned it the best I could in my driveway (ignition timing and mixture screws) and then I hit the road! It ran flawlessly the entire trip. Even when I busted my transfer case on Golden Spike trail and had to wheel haphazardously into the night AND then also finish Gold Bar Rim the next day, all in 2WD... The SMI Qjet never gave me ANY trouble whatsoever, even though my rig had a major handicap.
I cannot say enough good things about SMI's product and their customer support.
You open the box and the carb looks brand spanking new too. Like you bought it from GM. Keep in mind that ANY carb will require some tuning by the end user. NO carb will be setup optimally out of the box. Its up to you to get the correct jet size and mixture tuned on your engine. I sent SMI's tech guys a readout of my engine's vacuum measured at progressive rpms (since I don't know my cam specs). They used that to determine a jet size for me.
I hadn't started my truck for 3 weeks here. I went out yesterday, and while standing outside of the cab, I pumped the gas pedal 3 times by hand, turned the key for "1-thousand-1-1-thousand..." and it fired right up and immediately into the fast idle circuit. I didn't touch it for 5 minutes while it warmed up. I blipped the gas pedal by hand again and it settled down into its idle circuit. I'm sure the electric choke was still sorta opening too, but I drove it easy anyway and it never sputtered or stalled.