Suspension upgrade Qs for '65 coupe

[DeltaMustang65]

Got the export brace and monte carlo bar on with much pushing and pulling, and at the cost of a very sore back. Sometimes it just doesn't pay to be tall, heh heh...

I picked up an angle grinder from sears with some cutting and grinding disks and went to work on the old 4-piece. Fun times. If the old export brace wasn't metal, I would have loved to ritualistically burn it before tossing it in the garbage.

So the 5 leafs that come with mustang plus' "street heat" kit would be a bit much for a moderately modified (eventually) car? How about the 620 springs? They say that the 5 leaf mid-eyes and 620s drop the car an inch at all 4 corners. I'd like that, I'll check and see if I can get the same ride height with the 4.5 leafs. Would I still go for the 620 springs if I choose the 4.5 leaf springs or should I go with something less stiff? Also, if I go with poly bushings, is that going to rattle my car around like those ricers you sometimes see that seem to have no suspension travel at all? I'd honestly rather have rubber that I'd have to change more often than a ride THAT jarring.

I appreciate the answers, everyone. I'm thinking I'm gonna wait a month or two before buying a kit in order to give myself time to research this stuff. I want to make sure I get this done right before I spend a nice chunk of $$$.