@ billdutcher
Have a look in the custom tone section under Helix. I just uploaded a very, very basic extremely quick and dirty "SRV Lenny" patch which should give you somewhere to start. I also have to agree with the comments in the other posts here. Remember, It isn't down to just a single "magic" tone, SRV used various amps 'n' FX - Tube Screamer, Leslie, Marshall, Fender and of course the legendary Dumble. He had heavier gauge strings, plus lots of finger strength and a great deal of experience and technique and the semi tone drop in tuning. You could spend a fortune on replicating the gear he used and you'll never, ever sound like him - only an approximation. Helix is only one tool to start you on the path, let us all know how you get along with it - Enjoy!