I dont understand what you are saying about a pre-cut chamber but i guess that just the scotch, something i am guilty off sometimes as well.
On the ebay link you gave us it says 7/8x15x33.5 at the top. but it then says it s 10.5x 33.5 in the description.
If it is actually 15 wide, which i guess you checked, then you will be able to get two telecasters to fit onto that peice of wood, although it will be a tight fit. Then, from what you are saying, i guess you will cut two telecaster shaped peices of wood 7/8" thick and you plan on gluing these togther to make a body 1 3/4" thick. Thats fine and should work. If you want to route out each half of the body before you glue them together to make chambers, that will also work. So where does the pre-cut chamber come in!
It is possible to make a guitar this way but it is not going to be easy and made out of soild maple it probably wont sound great either, but thats down to preference.
It seems like you are going about this in a very difficult way.