There is a difference in measurement between the terms "spring arch" and "spring camber". Both are a height measurement, and both are referenced from the center mounting surface. Arch is measured to the center of the end mounting eyes. Camber is measured to the top of the main leaf immediately below the center of the end eyes. As such, if you load the spring until the main leaf is flat, camber will be zero, but arch will be 1/2 the diameter of the end eye.

For the MGA leaf spring in original form,
Free Camber = 3.60" (factory specification)
Spring eye = 1-1/4" diameter (0.625"- radius).
Leaf thickness = 7/32"
Number of functional leaves = 6

If you place the original MGA leaf spring upside down on the floor, then start measuring from the floor up, you get:
0.22 = Thickness of top loop
1.25 = Eye inside diameter
3.60 = Free camber
1.31 = Spring thickness (7/32 x 6 leaves)
0.22 = Bottom plate (short, flat, non-functional)
6.60 = Total spring height, not including center bolt

I have measured a number of original MGA springs to be about 6-3/8" total height, indicating about 1/4" of accumulated sag after decades of use. If you get measurements close to this, and both springs the same height, the springs are still in good condition. I still use my original springs after 50 years and 370,000 miles.

Quick reference for rear ride height on the MGA is to place your hand flat on top of the tire. The back of your knuckles should touch the fender arch. If you can't get your hand in there, the springs are sagging. If you have space there much greater than the thickness of your hand, then it likely has new replacement springs that are too tall. Front wheel arch will be it least 1/2" higher to allow for body roll and steering clearance over the turned tire. You may be able to place three fingers between the front fender arch and tire.

I did some measurements on my car with 165R15 tires (very close to original diameter).
Rear fender arch = 25=3/4"
Front fender arch = 26=1/4"
Rear bumper = 12-1/2"
Front bumper = 11-1/2"

Front wheel arch is 1/2" higher than rear, and front bumper is 1" lower than rear. I believe this is very close to correct original dimensions.

Addendum 3/12/09: I have collected the following information from the MGA Twin Cam Technical Data Book. Rear leaf springs are the same for all MGA models.

    LEAF SPRING
Width:      1-3/4"
Gauge:      7/32"
No. Leaves: 6
Inter-leaving: (none)
Distance between eyes:
    Free:                       41-3/16"
    Laden, at load of 450 lbs.  42-1/2"
Dia. spring eyes or bushing:  .860"/.865"
Average load rate:       125 Lbs/Ins.
Working load:            450 lb. at 3.6 ins. deflection

Notice that the nominal working load brings the main leaf to be flat. This is specifically why the free camber is set to 3.60", so the spring will be flat in the loaded condition. This gives the spring maximum stiffness and stability in the lateral direction for supporting side load during hard cornering. When some replacement springs are too tall they will not go to the flat condition when loaded. This will induce torsional loading on the spring during hard cornering, contributing to added stress on the spring material and slightly increased side shifting of the rear axle. It also raises the center of gravity of the car and the rear roll center, as well as reducing the amount of downward travel available before the rebound straps go taught. Significant negative effects on handling are discussed in different articles on this web site.