...Check this out:
SEQUENTIAL SHIFTERS - SQS & CARTRONIC MOTORSPORTS - PORSCHE SEQUENTIAL SHIFTER - PERFORMANCE FOR ROAD AND TRACK - Porsche Sequential Shifter System [SQS & Cartronic Motorsports] Distributed by AQ Performance
would be neat if they made this to adapt to the trans you're using now.
I've been told these guys have a setup that works with our ZF boxes:
Paddle Shifters, Sequential and Electronic - ASaP
I think whole-system price is in the $3-4K range.
Inverted Albins AGB10 is still too long for most (if not all) GT40 applications - even with billet bell housing 'as short as possible'.