Mike,
Not sure where you are located, but another option is the Bugat5speed conversion.
We make a kit for the 915 gearbox, but like ricola mentioned you will have to convert to IRS first to use our kits.
More info here:
http://www.germanlook.net/forums/showthread.php?t=10035
Feel free to email or PM for more info if you would like.
VR
ALex