Huh? What do you mean "takes off". Do you mean do we build LS motors now instead of gen1/2 SBCs then yes.

If you mean "do the LSx heads drop onto a gen1/2 SBC", then no, not at all. only thing common between them is the cylinder spacing. The LS uses 4 bolts per cylinder like a ford, instead of 5 like the SBC, the firing order is different, the valve layout is different (ports are symmetric vs mirrored), etc.

Firing order is something of an arbitrary thing, it's been done on SBC for some time.

There are small block Chevrolet blocks that accept LS heads (Bill Mitchell maybe?)

(note: I wasn't referring to box-stock LS heads on a box-stock SBC)

Mostly what i've seen is making the SBC take a symmetrical head. Saw some INSANE CFE pro stock heads at the machinist last year, he was building them in a large bore, short stroke deal setup for bonneville to run like 11krpm.