Well said, Br1ck. Yes, it was around the mid-70s that Westerly builds got heavier. The lightening of the guitars really began in Tacoma, as I recall; I don't think Corona had those changes on their plate, but Tacoma certainly did. For example, in 2007, Tacoma was able to implement the change to take the two truss-rod design of the 12-string necks to one truss rod flanked by carbon rods. This was then taken to its ultimate form by New Hartford where they had the coolest multi-axis neck milling machine I've ever seen (part of their Ovation history).
It's worth noting that one of the reasons Fender shut down Tacoma was that Tacoma's tool shop (among other things) was not up to the high frequency of change orders that the corporate luthiers were making to Guild. New Hartford really excelled at that, and that's primarily why Guild ended up there after Fender purchased KMC. Much of this stuff was related to revising the build specs to revert (sort of) to Hoboken or early Westerly production, i.e., "lightening."