Having just replaced the rear suspension springs on my chrome bumper 1973 MGBGT I have the opportunity to contribute some information on ride heights and the 7 leaf (6 + 1) springs both before and after replacement.
The replacement was due to both a newly broken 4th leaf on the Nearside old spring (see photo) and the usual worn rubber bushes and check straps creating a few warning noises:
For information, the front suspension is still on the original Armstrong Dampers but the rear suspension has pre-1998 Spax adjustable dampers with twin 5/8 inch bushes installed. The rear tyres are Barum Brillantis 2 185/70 R14 88T (run at 26psi) which I find are really suited to the car. They are on 5 inch Rostyles and I've never had any problems with the tube axle and rubbing on wheel arches etc.
For completeness but not altered in this work, the front ride heights on standard original suspension remain at:
No issues getting the old springs and thankfully the check straps off due to years of annual warm waxoyl application as per your recommendations. The old springs look original but from the known history of the car from a PO I know that these are the 1973 originals which were dismantled and remade by a blacksmith in South Africa in the early 1990's when the car was based out there for three years and springs and parts were hard to get due to the politics etc.
So....2x New 7 leaf (ACH31) springs (£35 for the pair back in 2011 via ebay!!) with rubber front eye bushes were fitted to both sides using the Moss SFK102 spring fitting kit that is based on rubber pads and bushes and new rubber rebound check straps were also fitted to both sides with the older Spax dampers reattached to the usual arrangement of the inverted and swapped lower Link Plates. New bolts, washers and nuts and nylocs were used all around.
Once the eye bolt ends were attached first, no trouble was had with getting the springs in place at the shackle ends or with bolting up the saddle and link plates and attaching the check straps ( with enough slack to have that s-curve in them at rest) and then reattaching the older Spax dampers. Waxoyl and copper grease (to threads) applied throughout refitting as per your advice.
Following all of this, the car stance looked much improved to the eye with a reasonably flat spring, slightly backward sloping shackles, curved check straps and no evidence of the "praying monkey" look that you hear of:
Following initial shakedown the new rear ride heights are now:
You often see questions asking what size and dimensions the MGBT 7 Leaf ACH31 springs are and have. Therefore after removing the old ones and before fitting the new ones I took various measurements and recorded them on the attached sketch, including the differences between removed old and new fitted springs and also the old broken and ok springs:
The old Spax dampers were "ok" but plans are now to compare/replace them with either some new GAZ rear dampers (One of the last GAZ2 Kits just acquired cheap for £60 as they ceased production of the MGB "kit" in 2019) and also some original Armstrong 8178LH and 8178RH lever arms that I have acquired in very good condition with correct resistance etc and taken off a 1969 MGB roadster back in 2013.