Thanks for the all the advice on the resins - this is indeed an interesting topic! I've done quite a bit of research on this and spoken to a couple of local guys who do this professionally - there seems no doubt that epoxy is a safer option...
BUT... I have two hurdles. The first is cost - I'm already looking at perhaps £600-800 for glasswork.
The second is unknown ability - not having done this before there seems little doubt that epoxy is going to be more sensitive to time and conditions. The polyester allows a greater variation in timing and conditions.
I think I've reached a compromise and this is the current plan:-
1) preparation - I'll need to have everything on hand and as mentioned best possible preparation of surfaces in terms of existing GRP keying and cleaning.
2) not to be over ambitious on first layers - small areas/quantities at a time!
3) all timber will be new, dried and prepared - I've been advised to store cut sections in the house a few days prior to using. There is a special resin preparation for wood that has been suggested to paint on first. This is thinner and soaks into the woodgrain. I'm going to do some testing on this first! Will post the details of this when I have the notes to hand as I can't remember what it's called!
4) I've been advised to use a woven glass tape and epoxy for structural joins - like transom and bulkheads - and then glass over this with the polyester before fully cured. Apparently this allows the epoxy to bond to both layers where there is any doubt about the bond? That said, the first guy who suggested this also had the view it was unnecessary for me as the boat wasn't epoxy to begin with and that it was only 'really needed' when bonding to old epoxy not old polyester. He was confident he'd go with polyester - but then added '...if you have any doubts...' Suffice to say that fueled the doubts rather than allay them!
5) no shortcuts or rushing...
Although I'm obviously 'very keen' (understatement!) to get her on the water, I can't seen the point in putting in anything less than 100% and taking the time to do the best job I can.
I've also kept all the large sections of removed fibreglass and will be doing some testing of bonding of various methods before I start.
The engine was said to have been rebuilt a few years ago and the drive replaced. This certainly appears to be the case and the drive is an AlphaOne not the original VP sterndrive...