Pics are kind of scarce from the day.

It's clear they had the gooseneck lifting fixture on the mantlet, but I've seem those on straight M1s also.

Additionally, the definitely didn't have the spacer ring around the base of the barrel at the mantlet.

I was told by the tankers that those with the railings that didn't go back all the way were ones that were retrofitted and had original turrets and the ones with the railings went all they way to bustle were the ones from the factory with the added armor.

I guess with such ambiguity about the issue, I can settle for using the old M1 as the base and reconcile any of my own doubt with it being something of a debate - hell, maybe there was even a mixture within the same unit as far as we know.

Not sure about the spacing issue, but I trust you as I know that you are very much the leading authority on this.

I always thought the easiest way to tell an IP was the turret overhang on the drivers hatch. On an IP the drivers prisms are about even with turret faces, on an long turret/A1/A2 the drivers hatch is considerably under the turret face.

Interesting historical sidenote:
The 2 Bd in Gelnhausen, Coleman Kaserne, held a competition between the D co 3/8 and and D co 4/8 cav and although 3/8 performed better scorewise, it ultimately came down to a coin toss to send 4/8 to CAT!

Tanks were IPs, I'd have to dig through mein photos to look at the specific details about armor thickness, but we had the side racks all the way back to the bustle rack. Oh,I have a TM but it is just for the M1, not the IP.

I was on D32 (LZ5200), or blue 2, D Co., 3/8 Cav (nee 1/33AR). We had red, white and blue for platoons, 1 was the Platoon Ldr, 2 his wing, 3 was the wing for 4, 4 was the platoon Sgt

Well this is fascinating. I was the loader on D-12 4/8 Cav on that awesome day! Just tooling around looking at pics and this thread was in the results . Kinda cool to have someone build "our " tanks !