My motors in the race boat sit low. Real low in the hull. I was going to use a 6" exhaust spacer to make up the difference but at first look I think I'm going to have to add a bit to that. Can i stack the 6" spacers like in the picture without issue? If not what do you beside having custom exhaust made that are not in the budget?

I have no idea how to post a PDF file... but if you google 86017200 ... it is a file from merc to installers it might help you... I think you can go up to 9" but double check that

the deal - try as little as possible because the extra weight of these extensions can cause exhaust manifold gaskets to blow out. Common on stock Mercruiser with the tall riser extensions to blow exhaust manifold gaskets even on brand new boats within the 1st / 2 years of ownership.

We do not even use OEM Mercruiser exhaust manifold gaskets nor their riser gaskets anymore - went over to Mr. Gaskets Ultra Seal II as they seem to hold up alot better than Merc OEM. Also proper torque on all bolts is important here when putting back together. Hopes this helps. Good luck