I think I qualify as the resident SET Brit car expert (4 Jags, 3 Rovers, 1 Lotus)
So, with that established, those old V-12's aren't worth owning if you aren't mechanically inclined. I don't mean 'can follow internet instructions' mechanically inclined. You need to be able to trace and diagnose issues without the interwebs, and use the net for confirmation.
If that's your case, fucking go for it. V-12's are cool as fuck and those old cars are straight sexy.
I had a MGB in high school.