Marshan always had a good reputation as far as i'm aware. They seem to have done OK in competition and many of the 80s boats are still about so that would indicate build was OK.
I have no idea how long a 19 would have been overall
No just bolt it straight on the back.
Unless you are going to be racing i doubt you will need a bow tank but if you do then Cyco on this forum makes some nice pick ups.