i have a 1954 G80S Matchless, essentially the same bike, was my second bike ever. PM me if you need specific info.
They are simply nice bikes, nothing more, nothing less, in all these years of increasing classic prices, they never really picked up in value.
Go to any brit bike trade site and you'll see they top out at 3000-4000-5000 and that's for a very original one. yours is far from that
On the other hand, dont think it'll difficult to find a frame....
If it was mine, would do it as a scrambler, as a bobber or cafe it'll look horrible (but what do i know...)
look for pics of a G80CS to get the idea