Congratulations on getting the full stack including the rack for the head. I have NEVER seen any of that gear in the flesh.
What happened with Thunderfunk was that Dave Funk was offered a chance to buy the remaining inventory of GB-440 parts from Gibson years after the amp had been discontinued. He then built some GB-440s himself until he ran out of parts. At that point he created the first Thunderfunk TB heads and over time made changes to the design to improve it, notably upping max wattage to 750W. An interview with Dave from 2008 is
here.
I still own an AMP BH-260, owned four different BH-420 heads (bought my first one brand new not long before the company shut down), and owned a XB-15 cabinet as well as a later flip-top cab whose model number I can’t remember. I’ve posted many times about A.M.P. here at TB. Do a search and you’ll find plenty of threads about it and the connections with SWR, Eden, Gibson and Thunderfunk. These amps are still out there and are great bargains. The speaker cabs are much rarer. The XB-15 in particular is very heavy but the design does sound great.
I’ve played all the heads but the Gibson and there are definitely some similarities in how each one sounds, but I continue to like the A.M.P. the most.