I would rather dangle my nuts in a Pit Bulls face than use powdercoating on a Brit bike resto !!
Cellulose paint can give superb results straight from a brush if you prep properly but, realistically, is it worth the time and effort ? Take it to your local car body repairers and get the spray guy to do it on the side for you in two pack - it'll look right and it's a mega tough finish ready to go in a few hours.
I brush painted my Matchless, every last piece of it, so I know it can be done with a brush but, man, it took some time and effort!