Dave H, the location of the spacer sets the ride height, as per the instructions. Later/current cars have a lower ride height at the front than the earlier cars such as yours at 1982.
Early 1980's cars like yours would have had the original Morgan rebound spring compressed by about 3/4 inch (= about 20mm) at static ride height resulting in a rebound spring installed length of 86mm - 20 mm = 66 mm. So in that instance the supplied 20mm spacer should go at the top above the little 'rate riser' spring leaving the SUPLEX 66mm rebound spring on its own at the bottom. Thus you will have the same ride height as you started with.
Later cars sat lower as Morgan fitted shorter main springs to try to get the rebound spring free. They nearly managed it but often still got the rebound spring a little compressed so still got a hard ride. In these instances the 20mm supplied spacer goes at the bottom to match the original ride height of those later cars.
So what is the difference in characteristic with the two different ride heights? Well the initial ride will be the same for both ride heights. The rate increase as the upper 'rate riser' spring comes in during cornering or big bumps will be the same BUT due to the reduction in bump travel with the lower ride height of the later cars the damper bump stop will come into play sooner in bump. That is the penalty of a lower ride height and less bump travel.
NB there is also a small potential risk that is difficult to quantify, but if one sets the ride hight lower than standard it is remotely possible that there will be tyre to wing contact in extreme cornering with bump. Just something to be aware of.
You also have an issue at 58mph I read. Puzzled that you think the nose is nodding but then you mention the effect of the steering? I do not really understand your wording, sorry.
Do you still have the original friction dampers or have you converted to the ball thrust races? If you have the ball thrust races and have not fitted a hydraulic steering damper there will be steering shimmy at between 55 mph and 60 mph that may be causing your concern/observation as that may set up a nodding effect too. If you still have the original friction dampers then check their adjustment.
Damper top rubbers. SUPLEX suggest setting these only just nipped up. If you are getting nodding still, then screw down the M12 nuts on the top damper stud by another two turns to more firmly compress the rubbers and try that, as that will stiffen the small displacement response of the damper and help damp out any nodding.
What tyre pressures? Try 22 psi at the front 24 psi at the rear.
Tracking will change with ride height so make sure yours is still in spec.
I hope this helps, best regards PJB.
