T. Albers -- thanks for the info on the various UP observation cars -- quite a variety, including - indeed - boat-tail cars. Who knew... (not me in any event). The last one you show with the round windows looks very "Art Deco-ish", I wonder if it was designed by Keene, who had designed some motor cars with, IIRC, round windows (and a tapered tail).
One of the current UP tail-end cars (the only one??) -- the Kenefick -- as it appeared as part of the 4014 tour (note the drumhead) - we saw it in southwestern UT a few weeks ago. This picture was taken in the big town of Modena (pop. 21), where there must have been over a 1000 people trackside waiting for 4014 (it was a 'lubrication' stop). This picture was taken 'downstream' of the crowd as the 4014 was headed out of town.
Indeed, the old CB&Q CA Zephyr vista dome/observation car is the Silver Solarium (apparently the only one remaining out of seven built). Its now owned by a private company that does rail charters. It was built in 1948 and refurbished a few years ago (my aspiration doesn't extend to doing the interior...). Here's a link to some nice interior shots http://www.libertyship.com/LA_.../Silver_Solarium.htm and more detail.
Carl -- my original thought was to do as you suggest, cut a hole in the top of an existing observation car and insert the dome (even easier with the successor passenger cars to the Al ones, as they were made of plastic). But I like the 'more authentic' look of the smaller windows (where the passage way goes around the stairs going up to the 'real' dome) and, of course, having the dome offset. The smaller windows are only available on the Al cars -- the later plastic versions all had identically sized windows the length of the car. The pictures below show what someone else did (a nice job IMHO). When Gilbert built the Flyer Al passenger cars, the ends of the cars, including the boat tail, were cast Aluminum with a small flange that fits inside the Al car body and is held in place with the screws shown in the top views (hardly prototypical...!). The geometry of the window placement and the wheel 'well' forces one to make a cut just before the last window of the original dome car - even though the wheel well is a bit elongated.
The other thing that these photos show is the good job the person did in polishing the Al (I don't remember where these photos are from -- eBay I think) -- I have a jar of Mother's Al and Mag wheel polish all ready to go...
