Bill,
I personally own the B&O LGB ABA set and I also own the complete LGB passenger set (3 passenger, 1 observation, and 1 vista dome). I also own a B&O USAT RPO car so I can speak from first-hand experience (I had this exact dilemma). The B&O ABA set comes up semi-regularly on the secondary market but it took me considerable time to locate the corresponding LGB coaches. I found the complete 3 car set at the 2015 East Coast Train Show in York, PA. The ABA + 3 car consist looked “chunky” to me, too much motive power in relationship to the consist of 3 coaches. When the opportunity to purchase 2 additional coaches arose, I jumped on the opportunity. When put together, the ABA + 5 coaches make for a gorgeous consist, but it’s MASSIVE so a large layout with a wide radius is suggested. The train will operate on LGB 1100 series track but it looks awful; I recommend LGB series 1600 track. I have a couple pictures posted of the LGB B&O set.
Anyway, I digress. To answer your question, I purchased a B&O USA Trains Railroad Post Office car, thinking I could add it to the LGB set. It looked God-awful. Don’t get me wrong, the USA Trains RPO car is beautifully made and has more detail than the LGB set, but I would NOT suggest mixing and matching in this circumstance. You can get away with mixing/matching USAT and LGB when it comes to freight consists without much of a “scale” issue. I’ll admit, the LGB B&O passenger coaches are difficult to locate and pretty darn expensive. I cannot prove it, but considering how infrequently the B&O passenger cars appear on the secondary market, I would wager LGB produced far less of them than other in other road names like PRR and NYC.
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