The 1250 and 1000SS both have a similar-style distributor which will separate from the distributor drive, same as your 1100's dual-points distributor.
The body of the distributor is different, though. But still has the same 4-bolt pattern. The distributor in the eBay link isn't one of those, however. Looks to me it's just an old dual-points model. In the "SS" models the side coil wire on the cap is not used and has a blank plate over the hole.
You'd definitely have to use the later-style CDI switchbox and a compatible coil. I'd use the coil found in '72 and later models 'cause it's a lot smaller and easier to find a good mounting spot.
Here's a few dist parts I found, so you can get a rough idea of their appearance:
http://www.ebay.com/itm/220955022807
http://www.ebay.com/itm/220955019943
http://www.ebay.com/itm/220954958924
http://www.ebay.com/itm/290671202460
http://www.ebay.com/itm/220954992140
http://www.ebay.com/itm/290377616012
http://www.ebay.com/itm/221707555098
Couldn't find an intact distributor on eBay. You might have better luck trying to locate a parts motor on Craigslist. Distributor prices have gone up astronomically; I used to buy 'em for $25-$50 but those days are long gone! If I recall correctly, the last models of the 1000 had the later-style round distributor cap with a clamp. You'd need the entire distributor for that, as it's all one unit. You can probably find a parts motor for cheaper than buying a used dist. on eBay.
Note that you could turn your 1100 into a points-triggered CDI system by using the later-style CDI switchbox and coil. You'd jumper the brown and white terminals together on the distributor-side (port side of engines using the switchbox) of the switchbox, and then take the (2) points wires coming out of your distributor and connect both wires to the remaining black terminal. Delete the ballast resistors and all associated wiring including the 2 old coils. Connect the switched power lead that used to go to the ballast resistors to the Red terminal on the switchbox. Run a jumper wire from the "hot" battery terminal on the solenoid, to the White terminal that's on the same side of the switchbox as the Red terminal. Blank off the side electrode, as it's no longer needed.
That's just an overview, I may have forgotten something. You're basically replicating what Merc did to make the first points-fired C-D ignitions. These systems fire when the points close, and points life is increased dramatically due to much less current flowing thru the points. You could set 'em up and probably never have to touch 'em again!
Many Many Moons ago I adapted a 1150 distributor to an old 100hp and as I recall the rotor shaft was too long. Had to cut a bit off the top but it did work. Or maybe it was a 99-c.i. rotor in a 90-c.i. distributor! I guess you could do some measuring to see if a later-model 99-c.i. distributor would fit.
Well, there's a few ideas, HTH & have fun experimenting!!.............ed
