Boy would I like to see a picture of that 389 in your truck, bigbadswingdaddy! Can you post something?
I've got a Pontiac 455 overbored to 465 in my '68 Firebird and get a very similar 13 mpg on the highway cruising on 3.08 rear end gears. Yes, a bit tall, but the motor has the torque and it doesn't feel tall at all.
Anyway, back to the original question, did you look into Accel and Holley for their TBI fuel injection systems? There is an advantage. Fuel mixture is always correct, at any altitude. I might make the change myself on my Firebird. Their EFI systems are a little over a grand, if I remember right. Check Summit Racing.
