FMS F springs - coupe only?

I'm looking at buying some drop springs for a cruiser project i'm working with my brother on. The car in question is an '83 Mustang hatch which will be used only on the street, we're upgrading to 5 lug and thought the springs should be addressed at the same time. The idea here is to make a nice comfortable cruiser with good power to enjoy driving. Nothing harsh. I've been reading up on the FMS B springs which I liked due to their similar to stock spring rates but then I stumbled across the F springs. The specs are below for those who are unfamiliar. My question is why are they designated "only" for a coupe? Neither the B, C or G springs show this designation.
M-5300-B ➅ 1979-04 ➄ .875" ➀ .5" ➁ 425/530 200/300
M-5300-C ➅ 1979-04 ➄ .875" ➀ .5" ➁ 650 200/300
M-5300-F ➂➅ 1979-04 ➄ 1.2" 1.0" 460/570 170/310
M-5300-G ➃➅ 1979-04 ➄ 1.2" 1.2" 500/570 170/310
➀ 1994-04 models – 1-1/8".
➁ 1994-04 models – 3/4".
➂ Coupe only.
➃ Convertible only.
➄ Will not fit 1999-04 Cobra.
➅ Due to vehicle assembly tolerances
these specifications may vary.

The range for the rear F spring is 170-310 and makes me think that the spring is much more sensitive than say a 200-300 as one from a B,C kit. The Vert kits from Eibach have spring rates that seem to favor a similar rating(170-310) so i'm assuming it has nothing to do with rigidity as coupes and verts could not be further apart on the chassis rigidity scale for foxes. Suspension wise I know the cars are identical but i'm nervous to drop the money on something I'm not familiar with. Does anybody out there run F springs?

No one runs or knows someone with F springs?

ttop88 said:

If you like the look of the B spring without isolators. This is the spring for you. The weight differance between the two in my opinion isn't big enough to tell a differance unless you take it to the track.

Click to expand...

Actually it's the slightly lower ride height I like about the F. I agree the spring rates are so close they will feel nearly identical in the driver's seat. It's been frustrating trying to find a car with similar size wheels and an LX body running the springs in question but the look you've achieved on your white LX is exactly what i'm after. Some people's cars who aren't running isolators seem higher in the rear though than others but on a GT I think the body mouldings may be fooling my eye. In the end i'll probably end up with the Bs if for nothing more than the much cheaper price. Thanks for all your help ttop88 and iwashmycar on providing great pictures.