• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

adapter?

If I were doing this I would procure some octal tube bases. Either salvaged from old unwanted tubes, or buy new one like these.

http://cgi.ebay.com/Vacuum-Tube-8-P...ryZ73375QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Then I would get some 5 pin sockets to fit the 807's, and using short solid copper leads soldered to the 5 pin sockets, mate them up to the tops of the octal bases. The only tedious part is making sure the wires go to the correct pins in the octal base. And this, of course, assumes you are deft with a soldering iron.

I actually made adaptors like this with 4 pin bases years age for testing purposes. A little gorilla glue helps hold them snug.

edit: I forgot to mention that you'll have to drill a small hole in the side of the octal bases for the plate lead. I'd use Belden test lead wire for the cap. Or teflon coated silver plated wire if you're of that persuasion.

Victor
 
This doesn't solve your problems but is a definitely God's gift to mankind.
Aluminium plate. When covering up ugly chassi holes or swapping from one tube socket to another these aluminum plates both helps cover the old or ugly hole, and serves to keep the sockets in place.
Howevere there weren't any for 807, but there are plates you can custom drill.