I've always found "price comparison" sites pretty expensive for classic cars
Absolutely. I've found comparison sites to be a complete waste of time. Try ringing up insurers who are likely to understand what's going on, footman James, Peter Best, Adrian Flux. I'm 24 and I've got the landy (just like your bottom quote) on Adrian Flux for £160 for the whole year valued @ £1K. Footman James do my Midget, £500 ish for the year valued @ £7K. That's with all (rather extreme) mods declared.
Stuff that's cheap to insure is often a bit random, You've got a good list there, try spitfires, dolomites, midgets as well - you might be surprised. Rack the annual mileage down and the excess up (while remembering what that means) and avoid expensive looking things like massive windscreen cover. Always get an agreed value - not just write in the box value but a proper one with pictures - it's worth it's weight in gold if the worst should happen.
When phoning up I found ot pays to interrupt their silly script at the start and just say: Right I'm 24, car is over 30 years old and its
heavily modified - can you insure me? That saves a lot of the faffing about for them to just go NO!. Try and get pre-1973 and you'll even save on road tax
I've also found that fully comp is cheaper than TPF&T. Weird.