I can add that Tannoy had a MAJOR rethink of the DC concept in 1980 or thereabouts and the "tulip" waveguide as used on the smaller units was one result. The crossovers were totally re-imagined as well, the nasty and lossy rotary switches being replaced by the gold-plated screws as used on the modern ones. I understand the tweeter integration was totally re-done as well in the 80's and the results of this work is beneficial to older drivers (ask Lockwoods as they can re-build and service both crossovers and drivers).
Until recently, the HPD drivers with foam surrounds were shunned by the cognoscenti in favour of the corrugated surrounded drivers from the previous Monitor Gold era. Now the prices are going through the roof, the HPD series are rapidly climbing in value and this is even working down through the plastic coned versions (I LOVE DC2000 and DC3000 models, so big hearted and involving and LOUD!!!).
Do what Dave has said. I'd try for some Monitor Golds and expect to spend money on the crossovers. Lockwoods can completely re-cone the HPD's and these drivers are taken further than when new. The HPD's have slightly less sensitivity (not really an issue) and higher power handling. Someone said that Tannoy will fit the previous cones/coils with corrugated surrounds too, so best to ask them I reckon..
P.S. I think their add-on Super tweeters are there to smooth out the pepperpot tweeters as much as anything else, but you've got to get the standard speakers sorted first and it won't be cheap.....
I can't go on and I can't go back, I don't feel so matter of fact,
I tried and tried to make good sense, What's the good to try it all again?