A project I'd like to see from Jens...

[RedskullDC]

Hi freqmax, et al.

New production run of 6581 ...

You could theoretically already make "replacement" 6581's.

VHDL code for 6581 equivalent is available here:
http://code.google.com/p/netsid-papilio/source/browse/trunk/doc/original_sid_src/sid_6581.vhd?r=2

Use a GODIL module:
http://www.trenz-electronic.de/products/fpga-boards/oho-elektronik.html
(250 model should easily suffice).

They're a great little product for replacing obsolete/impossible to find DIP parts.
I've used them a couple of times for repairing late 70's pinball machine boards.

Not a trivial solution, I grant you, but do-able.

Cheers,
Red