Bob---Delco products have found their way into other parts of the
Triumph, but to my knowledge only Lucas made the distributor. Their
numbers run from 40033 to 41398. Since the shaft of the distributor you
now have fits the pedestal, drive gear etc. it could well be from a TR
of another model, as the GT6. If you want to spend a few more $$ order
a cap for one of these, or ask someone at TRF for the dimensions of the
GT6 and compare it to your 'old' one.
The bob weights and springs control the advance curve of most
distributors, with some influence from vacuum lines, if connected. Since
your distributor is thought to be non-standard, who knows what was done
to the advance mechanism. There's about 20 deg. of advance 'built in' to
the 1973 distributor. You could check how much you have from idle to
3,000rpm, with a timing light. It could still be non-standard at
intermediate rpms, so it depends on how important it is to you to follow
the factory settings.
Eventually you'll have to get a cap to fit the distributor that's in the
engine, or bite the bullet and order a Lucas rebuilt from your favorite
If you want to compare what you have with the Lucas, pick up a copy of
"Tuning Lucas ignition systems" from Speedsport Motobooks, Bercourt
House, York Road, Brentford, Middlesex, TW8 OPQ, England. A good book
to have around...