i have a 65 mustang 289 c-4. It has 235 60 15 bfg radial t-as on the back. I have 3 leaf grab-a-trak springs and shocks in my rear. This combo worked ok till i installed two 12 inch subs and amps in the trunk, now the car sags, bottoms out on bumps and the stance looks terrible. Two questions, should i go with 4 or 5 leaf springs, I have heard 5 would be very stiff but would 4 be stiff enough? And has anyone used jrs springs from laurel mountain mustang? I found a set on ebay for a good price but have never heard of them and wanted some feed back before buying them.