The buick regulator won't work on a 4.0 because the adjusting screw would point straight down and wouldn't be accessable.
You can use the Cartech #2025 or #2027 which is an FPR/FMU but if used with a standard n/a engine just a FPR. There again why? If you need more fuel step up to 24 lbs injectors and then lean it out with your chip programming if thats your problem. Also, unless your running alot of mods on your 4.0, more then the standard bolt ons, I see no need for such.
Later Doug904.