Does anyone happen to know of ZZP'* underdrive water pulley for Series II'* will work on Series I'*?

I don't know for sure, but you could help me figure out. Measure your stock water pump pulley for me, and make sure it has 4 bolts in it with the same pattern as ZZP'* pulley. Then I will measure the pulley on the GTP or SSEi, and tell you if the measurements are the same. If they are, then you should have no problems.

These are approximate, best I could get.

Center Hub 2.5"
Bolt pattern 3.25" Approximate from center of one bolt hole to canter of
hole across from it.
Overall diameter 5"

I just quickly measured the stock WP pulley on the SSEi, and all the measurements look to be the same. Unless GM decided to change it by a few mm'* or something, I think it is the same, so you should be safe going with the underdrive. I also couldn't get exact measurements because the engine was still hot, and I don't like burning myself, but my measurements very closely resemble yours, so I would say they are the same.

Do you think I would need a shorter belt if I used it. I have a 2.25" SC pulley, and just ordered the ZZP oversized tensioner and a Gatorback belt in stock size.

The supercharger has its own belt. That belt should be fine. Since the underdrive pulley is larger than the stock pulley, you may need a bigger belt, but according to ZZP, as long as all your other pullies on that belt are the normal size the stock belt should be fine.

Sorry, brain fart. I was thinking the pulley was smaller and on the same belt as the SC. I do know underdrive means bigger, but I wasn't thinking too hard.

You're going to have problems with the cross member I think. Don't think the underdrive pulley will fit short of the cross menber that holds the motor mount. Let me know if it works. Would like to try it on my 1998 SE. I've a 10% alt pulley and an underdrive pulley on my SE. Gained .127 in the quarter mile using them.

I have to check that. The Series I'* had a differnt motor mount/waterpump pulley relationship. One such that the mount does not have to be messed with to get the belt off.

Depending on the size of the pulley, there isn't much room to expand it before rubbing the mount, and it is on the same belt as the SC. According to another thread right now, it won't fit.