I checked out what I could here based on what parts I have.
Here is a photo showing the measurement I am taking. Basically it is the length of the inletting in the forend.
image.jpg
Early Meriden extractor splinter: 4-5/8 - 4-3/4"
Later Meriden extractor splinter: 4-1/2"
Meriden ejector splinter: 4-1/2"
Meriden ejector Beavertail: 5"
Reproduction ejector: 4-1/2"
And, while we are at it, single barrel trap with draw bolt forend: 5"
About the only thing that I can confirm from what I have here is that Meriden and Repro forend tang lengths within the ejector splinter category are the same. I would suppose that the BTFE irons are the same from Meriden to Reproductions. Maybe someone can measure the length of their Repro BTFE iron and confirm in the tang is in fact 5" long?
The extra length on the Beavertail irons is to make adequate room for the draw bolt to thread in. Since the forward latch screw is only a littl over 1/4" from the end of the tang on a splinter forend.