For structural 'surety' you need to exactly define the dimension of the deck, the dimension from the 'bulwark' to the coachroof being the most important.
A laminated decking needs to be very carefully engineered, as it is essentially a flattened or 'flat-plate' box-beam laminate structure with fixed 'ends' .... quite complicated to design 'well'. A good structural engineer can easily 'back calculate' the original 'intent' of the structural load bearing ability of the deck. So for an amplification to Jeffs recommendation Id further have the OEM deck analysed first, before taking it to a 'boat designer'. That will establish the strength characteristics/function ... and 'validate' the original designers/engineer's (important) FACTOR OF SAFETY. The factor of safety is a 'contingency factor' that is included in structural design so to withstand 'unforseen but probable' maximum loads. Most 'blue water boats seem to 'back calculate' to a Factor or Safety @ 3 or more, 'coastal' boats at 2 - 2.5 FS. etc.
BTW - you DO NOT want to use "mat" for this reconstruction, as 'mat' is only for 'cosmetic purposes', and is essentially non-load bearing form of 'fiberglass'. For this rebuild you want either heavy weight cloth or woven roving .... then maybe covered or overlayed with 'mat' as a cosmetic 'leveling or smoothing' layer. For an ocean capable boat the deck must withstand the impact forces of a large 'boarding/breaking wave' .... . ;-)
Ok, I'm not sure what you mean by bulwark but the deck has no coachroof. Rather, it's a flat deck with a deck-stepped mast (a challenge with this task) and only the raised pilothouse. The boat was built in 1974 and the builders are no longer in business (after 200-odd years), so if we're going to get further structural checks done, it'll need to be by an engineer.
Regarding the mat, we're looking to use 450g/m2 biaxial cloth, recommended by the West Systems dealer over here.
I'm going to lift a strip of teak on the aft section this weekend and drill a hole in the plywood below to get an idea of what we're working with. At the very least, the plywood will need to be removed as it's soaked & rotten to the core.