Is there anything special I have to do in order to put a set of LT-1 heads on an old style small block??

Yes - there is a lot of fabrication needed. The bolt holes match but there are extra cooling ports that have to be closed off, the heads are reverse flow so you have to deal with the waterpump and alt etc. as well as their mounting. You'll have to use an lt1 intake modified for a distributor and don't forget this is all fuel injection not a carb so you're dealing with that conversion too.

I think this is a popular 3rd gen conversion and from what I have heard it works well but I haven't really seen it in person or seen a price comparison.

don't even screw around with it. it's too much work, when a set of cast iron vortec heads are the same as the cast iron LT1 heads- and flow better than the aluminum LT1 heads and have better chambers.