Hi,
I agree, you are better off replacing those old shocks, if they are leaking excessively. You'll need to send in your old ones as cores. Or, you might just try putting in new oil and bench test the shocks to see if they are okay, before replacing.
I estimate the lever shocks on my car are at least 30 years old and they are still in perfect working order. I just replaced the oil in them. Meanwhile, a set of expensive Koni shocks on the front of the car for a lot less years, probably 10 yrs actually on the road, were worn out and needed rebuilding or replacement (I installed new Konis, but will have the old ones rebuilt as spares. The new ones are slightly different.)
Personally, I think lever shocks work well and have never bought into the need to change them out for "modern" shocks, along with all the re-engineering needed to fit those to our old cars.
The original rear lever shock used was an Armstrong DAS9, I think, on all the "big" TR series. A race oriented upgrade is the larger DAS10, but that shock requires a larger mounting bracket be welded onto the frame.
Another good source of lever shocks not yet mentioned is Apple Hydraulics, which also offers uprated versions if you want a heavier duty shock but still the standard DAS9 size.
www.applehydraulics.com is their website.
If you wish, it's also possible to simply replace the oil with heavier, for increased dampening. Try a motorcycle shop for 20W or 30W fork/shock oil (stock is approx. 10-15W, which Moss and TRF sell). I've heard of people using 40W and even 50W racing motor oil (non-detergent) in shocks, but that seems pretty extreme to me.
Changing oil is easy. Just be a little careful removing the large nut on the front/bottom of the shock, it has spring loaded components of the valve mechanism behind it that must be reinstalled in the right sequence. The filler hole is a smaller nut at the top/rear of each shock. Shocks are most easily refilled when off the car, in a vise or something to hold them upright. It's important to repeatedly actuate the lever while refilling, to work out any air trapped in the valve area of the shock. You'll also notice any grinding or failure of the mechanism, while doing this. (The movement should have steady, smooth resistance both up and down.)
Another option is a set of adjustable lever shocks, a modification offered only (to my knowledge) by Cambridge Motorsports in England. Pretty neat setup.
www.cambridgemotorsport.com is their website.
Or, it's possible to fine tune shocks using different valving setups. I've heard of using valves from MGB front shocks in the rear Armstrongs on TRs, for about a 25% increase in dampening. I haven't tried this.
One suggestion that might make your life easier. Replace the bolts holding the shocks to the bracket with 3/8" NF socket-headed bolts. It's a whole lot easier to get a hex/Allen wrench into that narrow space, to tighten and loosen the bolts. Use a nylock nut on the back side of the bracket. I recently made this change and it makes the shocks so much easier to remove. Just be sure the shank of the bolt, the unthreaded area, is long enough to keep threads out of the hole in the shock and the bracket. All the knocking about that shocks get, threads inside there will grind the oversize holes mentioned in the article referenced earlier. You might need to add a washer or two to fine-tune the fit of any bolts you find.
Cheers!
Alan