TR-4A and TR6 clutch covers (pressure plates) are essentially the same. Unless you're building a race car, do yourself a truly huge favor and wait for an N.O.S. Laycock clutch cover to come along on Ebay (or wherever) if you want to retain the original diaphragm-spring clutch. Even a good used original Laycock clutch cover is worlds-ahead of the overly hard (stiff spring) units being sold these days.
If you have a TR-4A, you can also consider switching your flywheel and clutch disc with one from an earlier TR-3A or TR-4 (which also requires switching the transmission "nose" housing and throwout bearing assembly for the earlier type). Sounds like a lot of work, but it's not. This "fix" would not apply to TR-6 cars, though.
My 2-cents anyway.