I tend to disagree. The swap may work between a Parker #2 frame and a #1 1/2 frame, but if your friend found good wood from another #2 frame Parker G grade, chances are it would fit very well. This is because most of the makers of vintage U.S. doubles were using machine made stocks. It is common to see machining marks in the inletting. I have to say I do not know if there are dimensional differences between #2 and #1 1/2 frames of Parkers.
I learned this right here several years ago when I bought a Lefever DS-E action and forearm at a gun show. A few weeks later, at another gun show about 60 miles away, I found a very nice Lefever buttstock for $15.00. I took it home and tried it on a small XX frame 16 ga. G Grade action, and it fit perfectly, well within normal tolerances for factory inletting. Then I looked at the serial number in the wood, and it seemed very familiar. I got the 12 ga. DS-E action that I bought a few weeks earlier and found it had the same serial number. These guns were a small frame 16 and a standard frame 12, and the serial numbers were years apart, but the fit of the buttstock was identical.
I asked the question here in this forum about machining marks in inletting and whether U.S. shotgun makers used duplicators, and several guys provided information and even photos of old multi-head stock duplicators. Finishing and checkering were done by hand. Duplicators are not created equal. Some provide a drop in fit while others will require some hand fitting. Mass production and the concept of interchangeable parts was already well under way in the U.S. gun industry. There was still a lot of expensive hand labor involved, but it was largely eliminated where possible.
