Tried wheeling the bike with the toggle chain bolt removed, and it seems fine. It is best just on the front wheel and brakes didn't bind.

So I might consider going down the two speed wheel route if I keep the bike. Would prefer to go for brifters working two speed drsaillers and another an steven perry or (cqp??) Front mech mod. Ie four speed using single speed hub.

Its possibly a long term alteration as my mezzo needs finishing first.
And I am enjoying my downtube FS most at moment!!