Boring mills do come apart fairly easy. Most of the parts are keyed to go back as they belong. I would consider having the rigger "tip" the machine through the door way, not a big deal on a smallish mill. Even if you need to remove the table and saddle, its a pain to remove the drive shafts and screw.
Devliegs come apart fairly easy also, the columngoe to the floor and is bolted and keyed to the base section on its face. I believe the drive shaft is splined to separate also. There is just some wiring to deal with.
Heres another thought on deciding what machine to pick. DeVliegs can only move one axis at a time, besides the quill. Theirs only one motor and it drives through gear boxes and clutches. Devliegs claim to fame was .0002 repeatability, nothing came even close to that at the time, most machines were.002 repeatability. The other big thing was auto position, you would put your end measure rods and micrometer in the v and the machine would move to that position, and even take out the backlash in the screw, ahh yes the pre CNC fun stuff. If you ever go look at a DeVlieg open the door on the back of the column, take a look at the number of relays in there, it can be a nightmare.
As for a tailstock, on a DeVlieg, you use the rotary table. Bore one then rotate and bore again. I knew of a job that this worked well for, a two inch shaft on ball bearings in a bored casting about two feet wide. They made thousands of them like that.
Old boring mills seem to be coming out of the wood work here, like Lucas 21, 22. Old stuff but useful for the right person, just watch the spindle speeds some are only 100 RPM.
I had an old Lucas 21 years ago, had a taller column, over sized table and the tailstock. Also had a factory installed motor and high speed option went to 400 RPM. I sold it off and bought a Cincinnati Cintimatic CNC that worked better for me. It was sort of a DeVlieg wannabe with a Dynapath 10 control on it.
If you are looking at Devliegs, Ive got TONS of info on them, specs, ect