Well, I have a 1979 F150, and around a year and a half back I had to do the heads after I lost a head gasket.
I was running the original 2 barrel and upgraded with a new #1406 600cfm performer and a used $40 edelbrock torker intake.
The intake is not best choice but the old beast runs down the road nice, and I get better mpg than I did with the 2 barrel...until I put my foot into it, that is. I'd like to upgrade to a 5 speed from a 3/4 or one ton 460 truck, but at that point, I would go with the full tilt 460efi and 5 speed, but I don't think for plowing the 5 speed is worth messing with.
If you are running a 351M/400, you honestly can't expect to get 20mpg with the C6.
Depending on the usage on the carb, a rebuild might be in order.
I know when I am pulling my car trailer, she runs fine down the road.
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eliteman76
1972 Torino GTS 351c 4v cj 4 speed
1979 F150 4x4
1992 Explorer
1999 Contour
<font size=-1>[ This Message was edited by: eliteman76 on 5/7/07 1:07pm ]</font>