Bobby, it's not likely that the hamon will be very pronounced because you're using a truck spring for the steel. Also, unless you're using Parks 50 oil, you probably wouldn't get all you can out of the hamon even using the proper steel for hamons. So dont expect a good hamon.
However, this is still a good way to help prevent warping and to get a great differentially hardened blade. So, yes, by all means clay the spine and ricasso area if you like.
Just plung the blade vertical tip first but dont go in past the clay and harden the tang. There's no need to harden any parts that dont need it. Anything that is up to critical and not covered with clay will get fully hardened.
Do your thermocycling and sand off most of the soot before you put the clay on.