The only small block gear drive setup I would use is the one from Milodon. I have one on my small block 408. However, I haven't personally heard my engine run, my dad did, and he said it sounded pretty cool! He liked the whine noise it made. As far as block mods, you will have to drill and tap the block for one of the mounting holes on the gear drive mounting plate. Other thing is you will have to shorten the fuel pump eccentric 1/4" of an inch.
http://www.milodon.com/gear-drives/gear-drive-ford-sb-chrys.asp