As people probably know, I'm very much into 'saving' old boat kits, and publishing plans to make them 'less rare' and I would endorse Arrow5's suggestion of copying the parts, drawing them up and building - if you want a built boat - from them.
If Phil Smith's son is still selling copies of the plan sufficient to build the kit, then I would not make the copy available. But quite often the old boat kits (unlike the aircraft ones) depended on some spindle-moulded balsa parts which were not defined on the plan. Feltra kits, for instance, just had assembly instructions, as, of course, did EeZeBilts... If the kit is like that - one where you really need the actual part shapes in order to make it, then I think there is a case for making the copy available to other modellers.
Luckily, in this case, you can easily ask Phil's son how he would feel about this. I would have thought he would be quite happy if it was a case of saving an old design that would otherwise be lost.
Of course, if the plan to which he holds copyright does provide all the constructional details then you should not make it available....
