Repros parts interchangeable with Originals

[Quail1]

I was just rereading Nick Sisleys article on Parker Reproductions from February 1996 SHOTGUN SPORTS.

In the article he states "These are exact replicas of the originals, and I'm told that many parts are interchangeable".

I just tried putting the forearm from my 20 ga Repro on the 20 GHE, and vice versa. The Repro forearm would fit on the GHE, but the fore arm lever wouldn't close. When putting the GHE fore arm on the Repro, it simply would not fit on. Visibly they are somewhat different.

Does anyone have anything to offer as to the interchangeability of parts between guns?

Specifically I'm wondering what is the likelyhood that a Repro stock(straight) would fit an Original of the same gauge?