'67 GS400 rear sagging

So I got my car back together and the engine back in, using the stock coils, both front and rear and it sags slightly lower in the rear.
I'm guessing this is normal for 44 year old coil springs? The fronts sit perfect, but the back is to low for my taste.
I'm thinking about buying new rear coil springs, but I don't want to waste my money if the new ones won't bring the rear up to at least the same height as the fronts.
Should I get the stock constant rate Moog coils? or the variable rate Moog coils?

I just dont' want to waste money. Any tips will be appreciated.

Thank you,

 

I purchased the set advertised in the GSXtra from the GS club, so far I have only installed the rears, but I like them a lot, ride height seems normal no sag and nice riding. I think they are $210 for a set of four? I would have to break out a copy to verify that though. Mike

 

I bought some new variable rate rear springs but the back still seems to sag. But looking at the rocker panel it appears to be exactly parallel to the ground. Is this normal? The front springs are the original factory ones. The rear end is 8.5" out of a '72 skylark. Is there some sort of spacer they sell for the rear springs to boost the height about an inch or two?

Thank you.

 

That pitch comes from the factory.

These coil spring spacers lift the rear: http://www.ebay.com/itm/2-REAR-BILL...s=63&clkid=1226100027083783730&_qi=RTM1039513

 

Thanks Joe, I appreciate it!

 

eaton spring in detroit could fabricate u springs. isn't the rear supposed to sit a little lower than than the front?

 

I think the factory height in the back and a lowered front would look good.

 

If you look at most '60s Skylarks they were ass draggers. I bought a new set of Springs, Bilstein Shocks and a 1 1/2" lift kit from Mr. Lift Kit in Texas. His name is Harlon, great guy. Now the ends of the chrome body spears are the same height off the ground. And Yes, That was the Factory set-up. Had something to do with aerodynamics.
PONCH

 

I picked up a set of cargo springs from NAPA and it brought the rear end of mine up, in fact now it's an inch higher in the rear than the in front when measured at the rocker.

Thanks,

 

I'm not sure how much more a 340 weighs than a 300, but on my '66 it has an awesome looking stance (for a 4-dr too!) with everything as it was. The springs are still factory (the original owner kept with the car a small notebook with all the repairs he had done from 1966 to 1996!). I think the 14" wheels in front and 15" wheels in back give it a little lift in the rear.