I've had a bit of a rummage about (and bought an MC 50mm f2.8 after a long search). It seems that the cranks and waist level finders didn't change (assuming the ETR I found listed on ebay was as original as claimed), chrome-rimmed lenses were indeed the norm.
The original 75mm lens will have to wait now as this month's budget went on the 50mm (more useful!) I now have 50/75/150/200mm for the system, the middle two are PE lenses while the 50 and 200 are MC. I know this plan will end with two 75mm lenses but hey, I want to reassemble an original outfit.
I have a bit of a mixture of kit as I bought an ETRSi with 120 back, 75mm PE lens, WLF and crank, then added a speed winder (which I suspect is older, it's just marked ETR though), an unmetered prism, then a metered prism, 150mm and 200mm lenses, and a couple of extra 120 backs.
Apparently there was an AE prism which worked fully with the ETR, but the AEII (and AEIII) only work fully with the ETRS/i. The AEII will meter on an ETR but you have to use it in manual mode and press the button on the front to meter - it won't switch on when you half press the shutter like it does on the ETRS/i. I tend to use Sunny 16 with reasonable levels of success, HP5 is very tolerant!