I was looking at one of my street rod magazines today and came across this web site for hot rod batteries crystal cell technology??? http://www.hotrodbatteries.com/
One model (HRB 11) is even smaller (5.125 x 3.250 x 6.500) than the RSV battery(6.875" x 3.4375" x 6.125") with 375 cranking amps. Looks like the HRB 14 with 475 cranking amps would work too.
They don't advertise the price so I'm sure it must be kind of high considering a 100% replacement five year warranty.
Just thought I would through it out there for anyone who might be interested. If nothing else, I think I might look into one for my street rod.