I bought some near new ITS boxes for my Formula and after the fact realize that merc doesn't make a long input shaft for the B1, only the X series drives. I have a practically new set of B1 Swept back uppers that I planned on using but at this point I don't see how that is going to happen. Does anyone have any suggestions other than selling the B1 uppers and replacing them with X uppers.

I would think there would be a way to change the flange or the u joint to be able to run the long shaft on your upper.

The XR input shafts use a larger u-joint and I believe the gear end shaft diameter is bigger. The only thing I can think of, is to turn down the short end of the XR input shaft so the B1 gears would fit on the x shaft. You can do this with XR propshafts (so you can run standard Bravo gears) but I don't know if you can do this with the gear end input shaft.

It seems to be a rather complicated project. In addition to the above, you also can't just install an X input shaft because the retainer ring, as I understand it, is larger than a B1 retainer ring. You also can install the B1 ring on an X shaft because the yoke is too large and the spanner wrench won't fit over it. My head is hurting with all of these small yet road blocking differences.

The 336 formula for sale at shogren has bravos on imco extension boxes. How do they run those?

Imco makes their own shaft, but its longer. The ITS boxes are only 7" whereas the Imco boxes are 12". The shafts are not interchangeable.

So maybe shortening an imco shaft would be the easiest way to custom make a part?

Thats a pretty expensive option. IMCO wants over $700 for just 1 shaft, then the machine work to make it fit.

It's a boat...nothing is cheap lol. Prolly cheaper than the xr upper upgrade but you would also get strength of the xr too that way.

There are joints out there that are 2x2. (2 different sizes per plane)

You can do it by using an X gear set and the ITS u joint shaft.
Imco makes a retainer that will let you do that on the standard upper housing.