Hi Andy
Is this Glynns ELCO boat?
If so the full size boat is 80ft so a very rough guide to suit 6in figures would be 1in to the foot.
The model would be 80inches long (about 6ft 6) I cant remember what scale Glynn used but its not difficult to work out the enlargement.
As for engines……a pair of MAN diesels would do nicely……but failing this I would be looking at a triple set of Leopard brushless (DM is the man to ask but I would advise sitting down when looking at prices)
Hope this helps
Paul