Goldilocks and the three springs.

Best thing nowadays is the progressive springs.  I have used original V8 springs... too mushy.   600# lowering springs...too stiff.  Progressive motorsport springs...just right !

jeremy wrote:

I run the 620 grab a trak springs...I heard that for some reason they're not true 620's, and are a little lower rated, but IDK. 

I'm used to the break neck harshness of a lowered 80's fox mustang, so when I built my suspension on my 66 with 620 springs and kyb gas a just shocks, I found the ride to be very soft and compliant...Others may disagree, but for me, it's extremely smooth and forgiving compared to what I was expecting.  I have a lot of roller bearing stuff and mods up front, so that could contribute to my overall good suspension feel too.

The progressive springs indeed are great, I was running out of cash though, and opted for the good old cheap 620's

Gotta agree...  My 67 F/B 428 4 speed with the 620 springs /gas adjust KYB's and roller perch's and idler...close to perfect....jj
 

I'm with MS on this.  Progressives would do you a lot more good.  If you want regular springs, get GT's they are between stock and 620's.  They have worked well for me for low these 47 years.  620's work well, though, if you have the extra weight of a big block.

I used the progressive rate springs .I origanaly ordered them from Laural Mountain Mustang ,but they had trouble supplying them so I ended up getting them from summit. I have driven the car the ride is firmer than I as expecting. The car is not realy back on the road yet though.