I bought a boat that has SSM II drives. 2 previous owners ago someone welded extended anti caviatation plates to the drive. What would be the advanrtage of doing this? Only thing I can figure out would be it might be easier to get on plane. What might be the disadvantages of removing the plate and going back to the stock length.

I believe you are correct, the only advantage would be to get on a plane easier. If you are running the original 3 blade props and if the drives are pretty high, I would leave it as it is. If you are going to a more modern 4 blade then you may need to remove it to be able to get out of the hole. I had considered adding extended anti cav ventilation plates to my SSM3's prior to getting newer props. Now it hole shots without a problem (well it did last season).

Don`t remove it !!

If it ain't broke don't fix it.

And yes am going to be that guy.....it's an anti-ventilation plate not a cavitation plate.

There is always a grammer nazi lurking in the shadows.

Ok, I am going to be that guy again......it's not a grammar nazi issue, but using the wrong term nazi.... No Boating For You!