Anyway, here's an addition to the topic. It's nothing new, but I've remade one of the more noticable levels from Lemmings Plus DOS Project... no, not Oblivion (I seriously doubt that'd work on SMS, getting it to work on DOS was hard enough)... Variety Day! (PSYCHO 1)
It actually looks quite decent on SMS, as far as I can tell even with having to modify the level to avoid glitches there's no new backroutes (in fact, I think at least one old one is impossible on this version), and the original solution is 100% intact. I didn't even have to scale it down to less lemmings since the original level already only had 20 (although to be fair, the intended solution can be enforced with as few as 4 lemmings, so it wouldn't've mattered if the amount had to be reduced anyway).
Enjoy!
...by the way, out of interest, what would happen if you set (in the game data) an 'illegal' number of lemmings?