9 Bolt 7.25" Spider Gear Difficulties

I recently bought a Spider Gear set for my differential to change out.

My differential came with either a 9 bolt or 10 bolt housing. I currently have the 9 bolt differential.

So I took the Spider Gear Set to my Mechanic-Friend, who tells me later on that the shaft down the middle connecting the two upper gears is different than the one I currently have.

Here's a link to the product http://usastandardgear.com/ProductDetails.aspx?ProdID=12252

Now my problem is, the Spider Gear set was made for a 10 bolt differential. Can I just change the gears and thrust washers and keep the old shaft that fits in the 9 bolt, or is the kit completely not compatible.

If it doesn't work at all, where can I find a 9 bolt 7.25" spider gear set?

Thanks in advance!