Yep, you have the OD & ID correct. Depending on the od of your blank's butt section will depend on how big the ID of your reel seat insert will need to be bored out. I typically use Lemke hardware so I'll speak on his hardware. Depending on the OD of your butt section you would typically want either his LC 25 or LC26.
The LC26 is big hardware and you would probably need to go with an oversized ring or two on the end of the handle. The OD listed on the hardware is for the hood diameter and it tells you how big you need the cork to be inletted so it will cover the hood.
Here are a couple examples of some LC25 hardware. If you look at the upper end of the seat you'll see where the cork is over the hood. In order to do that the cork needs to be inletted to the proper diameter to cover the hood without having too much play around the hood.
Winston 12'6" 6wt. Spey
Sage TCX 6119-4 switch
For blanks (especially fiberglass and big speys) with a really big OD you might have to go with something as big as the LC26 so you can bore the insert out large enough to still have enough meat on the insert. Really big seats might require oversized cork. That way there is enough meat to cover the hood when the handle is shaped.
What size Spey are you building? Typically I have used size 16 and 12 strippers for my 7 weight and below Speys. I'll have to verify that tonight, but off the top of my head I'll stick with those numbers.
I only use Snake Brand Universals on my round rods and their standard guides on my bamboo builds.
Sorry, I only use Lemke hardware so I am out of touch with other manufacturer's hardware and dimensions. Feel free to PM me with any build questions so I don't hog your post.