I brifly swapped my SUs for a 390 Holley on an Edelbrock Performer manifold a couple of summers ago. The four barrel carb had distinctly quicker throttle response and it really changed the character of my '73 3500 automatic. However the accelerator pump gasket perished and leaked fuel all over the top of the manifold, when I sorted that out it became apparent that the jets were too large, but only when all the unburnt fuel in the first exhaust box exploded! I re-used bits of the SU linkage and made up a bracket, wasn't too hard. I've reverted to the SUs and the Holley is awaiting a strip and rebuild. I'd be grateful for any information about which jets to use for a 3.5litre V8 with a Kent 214 cam and standard heads/exhaust. I'd caution against using an Edelbrock 'triangular' air filter with the foam element, it catches fire if you get a back-fire and melts. I also had to remove the under-bonnet soundproofing to then fit a low profile 'pancake' style 10" filter.
Any tuning tips very welcome!