Thanks everyone.
It sounds like I should stick with the B6304S engine. Having a totally different computer is a major difference, among the others listed here.
I also found out that the S model has wider cam gears, a wider belt and they went from fiber cam gears to metal ones and from a 30K (or 50K) belt replacement interval to a 50 (or 80K) replacement interval (depending on who you talk to)!
Since a timing belf mishap (some dummy trying to save money by changing his own timing belt without knowing how important it is to have the three timing marks line up EXACTLY, (he was off by 2 teeth!)) is what killed the original engine, I'll go for the improved timing belt version of this engine.

P.S. Keith: thanks for your input - every car sold in the USA in the last 20 years or so must by law have a catalytic converter, so your G model must be a UK or Europe only model!
:)

Hello. Lots of different little things were improved. They added a nipple to the left side of block for the breather box. The tensioner hole was resized and a different tensioner was used depending on what year the block was used. The block also could be in a 94 model 960. The web casting on the right side of block was improved. The main bearings on the bottom side of the crankcase were changed from groove to no groove and the locking tab was moved to the center. The oil pan was changed several times for the oil outlet pipe was now in the oil pan instead of the block, "O" ring was now more crucial for the seal between the block for oil pressure. Cooling went from air to water cooled oil cooler. I am sure there were more little tweeks to the block that I no nothing of, but I have done some switching of parts around to make them all work in late or early model cars.

B6304F:
200hp high lift cams
OBD1
Bosh Motronic 1.8

B6304S:
180hp torque cams
OBD2
Bosh Motronic 4.4