a 144 Wieand Blower will produce 4-7 PSI of boost, and fit under the hood of your '68 C10, using a drop base air cleaner, and 2" element. gas mialage is figured in at 4% parasitic loss, that's what the holley manual says anyway. control the holley commander 950 TBI with a megasquirt EFI controller and you will have it made