Holly is known to over-jet their carburetors out of the box. I believe this is because too rich doesn’t generally harm a motor like a lean fuel condition will.
I also endorse Bob Oliver for tuning your Holley That is all he does. I had him blue print a new 670 avenger for my 404 Cleveland stroker. He had all of the engine specs and when I had the engine dynoed on a stand the operator was quite pleased with how the carburetor responded to mild jetting changes. He said he generally finds holly carburetors to be nearly impossible to tune.
your vibration could very well be coming from your half shafts. There are 16 sets of nuts and bolts that need to be totally tight or you will get a vibration just like you are describing.
insist on getting a full list of the components used to build your engine, suspension, wiring and any other work you had them do.
I think Forest may be onto something as most shops now do LS installations with in tank fuel pumps. They may have just done the same to you without thinking things through
good luck
Larry