Yes they are....my 2100 guides also will accept 1/2" bolts....
I will pass judgement on which bolts to use when we get there.
Since my 2100 guides had the 7/16" bolts in the 1/2" holes I really don't think the difference is going to be a worry.
What I found puzzling is the the distance between the uprights is about an inch wider on the 3700 guide....as compared to the 2100 guide.
The shape is different too....
I suspect the 3700 guide design was a step in the right direction to help eliminate breakage and possibly help stop tire sidewall damage.....
I can't be sure about the tire damage, but the weld area on the 3700 guide is a far better design....horizontal with the length of the guide as compared to the older 2100 guide.
Deeper skirt too will help keep the guides from wobbling on the grouser..
So far nobody seems to know the WHY DID LMC change the guides.
I have heard that the earlier guides were harder to make.....The forming die had a short lifespan ???????
I can't find anyone who can do much more than I have as far as speculating the WHY THE CHANGE.
The 2100 guide was not a stellar design from an engineering standpoint anyway.
The uprights were welded across the guide channel.....this can promote breakage.....and they did....
I will guess with you.......
I would love to have two full sets of 3700 guides.....but with one set of 2100 guides plus 57 guides we are going to roll with what we have....