I understand that Simon Spare's initial batch of 3 plank wagon kits has completely sold out. However, if there is enough demand he will run a second batch.
I have already put my name down for another as they are excellent kits and well worth having. I don't think it's a major task to finish them as the earlier diag 3 if you want to do something different with one. I'd suggest the main difference is a single set of brakes with no lever on the other side.
Anyway if you want one (or preferably several) please contact Simon to confirm your interest. (His contact details are included in my earlier post about the kits.)