E start crankcase vs non

I got a bunch of Norton stuff over 20 years ago and one of the items was a very nice bare 850 crankcase. I had always been under the assumption it was a 74, that is now in doubt. I understand that the 75 MK3 had some differences to tell it from the non e start ones. I've looked on here for details and only found a picture comparo with 750. I already know it is an 850, but how do I tell if it is a MK3 variant?
Thanks

I may have found my answer: the nons had 3 holes to mount the primary vs 4 for the e start. Is this correct?

My e start has 4 5/16 national fine threaded holes earlier had 3 1/4-20 threaded holes

RedBeemer said:

I may have found my answer: the nons had 3 holes to mount the primary vs 4 for the e start. Is this correct?

Click to expand...

Yes