IIRC i think cantefield(sp?) tried to make some smallblock SOHC hemi heads. I know Stage V Engineering made RB hemi conversion heads. FYI, the 5.7/6.1 isn't a hemi.
The 5.7/6.1 is more of a Hemi than any other 16-valve V8 that's been made for the past 30 years or so... it's just got dual plugs per chamber and squish pads added in ("bathtub" chamber). It's actually much better than a "true" Hemi and just about the most efficient way to make a two-valve combustion chamber.
Screw SB Hemi heads anyway. Technology and research has come far enough to where you can make pretty much just as much power with a wedge as a Hemi (at least as far as old-school V8s go). If you wanted to spend the time and money to adapt Hemi heads to an LA block you might as well just drop in a 5.7 or 6.1 and get lighter weight, better fuel efficiency and a lot more potential for big power (along with infinitely better parts availability and aftermarket support).