Not sure about Amod but there are some Bmod cars using tunnels as well as front and rear diffusers. All the top CSR's/DSR's in road racing have moved to tunnels but I think the jury is still out on how worthwhile they may be for Solo.
The front splitter/diffusers and rear diffusers are not too bad as far as packaging (and the rear can certainly help work a rear wing), but packaging a set of tunnels for Solo may be more trouble than they are worth. I'm sure there are more qualified opinions available here than this one!
Joe Gonzalez
1979 Legrand DSR- B Mod
Gilbertsville, NY