By the same process of searching through the forums, I found the Mac ONML graphics as well
Nice find! It's good to know we have all of these now

All styles are required to have low-res terrain, with high-res being optional. Since the Mac graphics are high-res only, we'd have to scale them down for low-res
Sure, good point.
Maybe once the tilesets are ready (I'm happy to help with the conversions wherever I can), we can have a poll to see if people prefer the Mac graphics vs. zoomed or upscaled DOS/Amiga graphics for hi-res. Sure, they're similar, but there are enough differences in the details that the tiles create quite a different look and feel which people may not prefer.
I myself am not 100% sure I'd want these
all the time, hence my suggestion to include them as separate styles. Since I use hi-res exclusively, it's of particular interest to me that we get this right; whilst I'm savvy enough to be able to mod the official styles for my own copy of NL, other users may not be.
They do look amazing though, and you're doing a grand job so far with the conversion. Be assured that the Mac graphics have my support, FWIW.
No matter what happens regarding the official styles, I am absolutely going to do the editing work purely for myself and my own copy of NL. So the question of how much work is involved shouldn't even come into play -- it is going to happen anyway.
Great!

Don't feel like you have to do everything though. By all means give me a shout if you need any help.
As far as the goal of matching the physics goes, it does that pretty much perfectly. I just don't like how it looks. But of course with high-res graphics operating with low-res physics, there's a trade-off between how good it looks and how good it matches the physics
As a hi-res user, I don't mind the way it looks at all. And, it's far more helpful to have the mask show what's actually going on physics-wise (which has always been the point, as I understand it). It means I never have to use CPM for this sort of thing (incidentally, I only ever use CPM for trigger points and to see what's what in new styles).
Frankly, I'm baffled that this is even a problem for some people. Lemmings is a pixellated game. "Hi-res" is something of a misnomer, in all honesty; sure, it's double the resolution, but we're still only dealing with tens of pixels even for quite large pieces.
I'm not saying your point is invalid, but it's hardly a comprehensive reason not to use the hi-res mode. You have stated that it's a matter of personal preference though, so... fair enough.