Standards form the basis of all engineering tasks. For a listing of Irwin standards prior to 1980:
Irwins 28, 30, 34, and 39
Irwins 37, 42, 43, 44, and 52
As with any long lasting engineering program, changes were made during the life-cycle of the product. Please join the Owner's Groups found on the Marine Sources Links page for updated info from other owners. They have probably done the same work and updates you are doing and can offer advice and photos.