Hi, I think I confused you with my numerous responses.
Because of timing differences between the Amiga and PC version, some of my earlier recommendations based on the PC version is not really valid for the Amiga.
So to be clear: for the Amiga, based on my experience, I'd say
the key thing to try is to have the second lemming flame-blast the pipe for the first lemming in front, at the place where you use the first flame-thrower. That way, the second lemming gets more separated from the first lemming (in other words, the first lemming reaches the pit earlier relative to the rest of the lemmings). This minimizes the number of lemmings in the pit when the bomb explodes, which in turn gives you a better chance of having more survivors.
But it's still not a guarantee, where and when you do the bombing still matters unfortunately. My current recommendation would be, after following the above advice, to "wait for first lemming to walk a step or two after he gets up, then bomb". In case you're wondering, the 58/60 solution is basically more or less the same, except you need to be super-precise in the timing and position of the bombing.
Basically it was not a very well designed level, that the first level in a tribes would have a solution that can be so unstable, and a gold medal requirement so strigent. No wonder they took out that level when they start porting to console systems. So, good luck!
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I never owned an Amiga, so regrettably, I just found illegal versions of the various required software on the Internet. Fortunately Lemmings 2 can be run directly from floppy and the floppy diskfiles can be downloaded from the same site you got the WHDLoad install of the game. So all I needed was the illegally obtained Kickstart ROM and then I was good to go. Yeah, I'm a bad boy.