Porsche transaxel numbers

I have done a search on the various Porsche transaxels and have not foound what I was looking for. Can someone tell me about the different transaxel numbering that porsche uses for it's transaxels and what has to be done to them to make them work. I am particularly interested in the 930, 968 and 996. I do know that the 930 is suposed to be one of the stronger units. ( got one but it needs some work to be in good shape). The 968 is a good unit but my local Porsche shop forman tells me that they routinely need to be overhauled after about 40K miles as one of the main shaft bearings begins to go about that time. I have a line on a 996 with only 100 miles on it, but I'm afraid it is a little pricey. Would that be a good purchase or should I just rebuild the 930?
I'm sure others would like to know the difference in the units and would like to talk intelligently when discussing them.
Thanks
Bill

I have used a Porsche transaxle in a mid engine application. I can't remember all the options but the G50/50 was considered the best bet. Extremely strong and also relatively modern. It shifted beautifully. Check out http://www.ultima-gtr.info/utips.htm#Transmission for a rundown on the various G50's available. I bought a adapter from Kennedy Engineering that needed a bit of modification but basically worked fine.

PS - Get the transmission checked out before you buy. Many are used for racing and are toast.