I am looking for advice about a Sunn cab that I have had for a LONG time. It's an 1x15 cab. It has handwriting inside that says it was built in December of 1968. It has its original, totally unmodified JBL 140F. Cone looks good...no tears or anything...amazing really given its age. This came with my a 40w Sunn head from 1965. This is the 2nd head they developed for bass at Sunn, basically within the first year of forming as a company. This was my first amplifyier, and I got it, well used, in 1972! This thing has lots of sentimental value to me...but facing facts, the JBL was designed to handle 150 watts. It has a beautiful voice at low volumes, but it distorts at whenever I turn the amp up much at all (I am using a GK 400RB with it now), even when paired with another cab. (the other cab is a beater Randal 2x10 upgraded with Eminence speakers...cab rates at 8 ohms/300w). I have been thinking of putting an Eminence Deltalite in the Sunn cab. The T/S specs (of course I am estimating) look good. I could keep the JBL in case I ever try to sell the cab to a collector. In the meantime, would this give me more headroom without distorting? Just as important...would I be committing a form of sacrilege? I mean...this is a classic cab, and a Deltalite is NOT classic. Of course, at 13, when I got the cab, my back was in better shape too Any advice would be appreciated!