Thanks for all the responses and great info guys (and so quick, too). I had no idea this was such an active forum! Nick, I did indeed remove the base plate before measuring, and there are no spacers, and thank you much for the warm welcome.
No worries Dan - 1) apparently this model comes in 3 different variations: 1/2, 1, and 1 and 1/2 HP, and I can't for the life of me find any distinguishing marks on mine (other than 25,000 RPM). 2) my router being hella heavy, I was worried about sagging/warping with a thinner sheet (although, in hindsight, maybe I could have gone thinner. 3) Bummer. 4) I didn't know that the router design (other than its own collet) dictated how thick a collet could safely/comfortably be used.
Tom, I've actually been looking at that model, and, if I can scrape the money together, is the one I'm leaning towards. Luckily I've not yet drilled my plate, but I do have those Bosch insert rings in my Amazon cart - I was going to use a hole saw in my drill press for the bit opening (I'm told to liberally use/apply machine oil when drilling) and rout the step for the insert rings (my machinist friends at the Banjo Hangout - which is where I've been getting my advice until now - say it should work fine).
Heya John, the Bosch is 2 1/4 HP - is that skirting the line regarding enough power? It does include 1/2 and 1/4 inch collet chucks, and a fixed base in addition to a plunge base.
Phil, it does indeed come with only the 1/4 collet and, even without the base plate installed, does not extend far enough, thanks.
Herb, I'm gonna be scrounging and scraping as is to upgrade my router, so I'm not sure I can drop 70 bucks on a chuck, thanks for the heads-up though.