I'm with Chris plenty of chemicals and then maybe a very light bead blast if you think it needs it.
The only ones I've done recently that were even remotely close to as pitted as yours were my Woodrup and my Claud Butler Buccaneer and both of those were chemical treatments only that didn't really need bead blasting.
The main tubes on both of mine came up surprisingly well but certainly on the Claud the pitting was worst around the tops of the rear stays and well the rear of it in general.
On dealing with the pits after cleaning I ended up using very fine finishing putty which was more like modelling putty as most filler is just too coarse to fill those small pits, the other option I thought of trying was seam sealer but I don't think that would work. Both took a lot of time filling, flatting, filling, priming, more filling and more flatting before I was happy enough to put a coat of primer on that I was happy to put paint on top of.
The only ones I've done recently that were even remotely close to as pitted as yours were my Woodrup and my Claud Butler Buccaneer and both of those were chemical treatments only that didn't really need bead blasting.
The main tubes on both of mine came up surprisingly well but certainly on the Claud the pitting was worst around the tops of the rear stays and well the rear of it in general.
On dealing with the pits after cleaning I ended up using very fine finishing putty which was more like modelling putty as most filler is just too coarse to fill those small pits, the other option I thought of trying was seam sealer but I don't think that would work. Both took a lot of time filling, flatting, filling, priming, more filling and more flatting before I was happy enough to put a coat of primer on that I was happy to put paint on top of.