The new Athearn/Roundhouse Oldtime HO passenger cars are based on the old MDC tooling. The biggest difference is the couplers are now body mounted. The are a bit sparse in roof details but have "glass" and nice filigree and striping.
I am using the Southern set. They have a simpler lettering scheme. I wil remove the lettering with 2000 grit sandpaper.
The biggest discrepancy are the 33 inch wheels. Passenger cars generally have 36 diameter wheels.
The couplers are body mounted EZ-mates with the wimpy plastic knuckle"springs". Throw them away. I am replacing them with Accumate Proto: HO couplers
The wheelsets on the Roundhouse cars are not a standard axle length. I am replacing them with Proto 2000 36" wheelsets. Most passenger cars are fitted with the 36" diameter wheels.
The truck sideframes are closer together than the usual truck sideframes. Care must be taken when reaming the journals out for the new wheelsets.
The journals are reamed with one of these truck reamers. Carefully insert the reamer into the truck and spin it carefully.
Spin the reamer in the truck frame. A chip should be generated. Carefully do both sides evenly fitting the wheelsets.
A chip will be cut out as the reamer is spun. I have found that when the chip goes past the tapered area it is time to check the axle fit.
Ream the journal holes until the wheelset spin rapidly. After both wheelsets are fitted the truck should roll on the slightest incline.
The new wheelsets will raise the car. The Accumate draftgear box and a .030 thick styrene mount will adust the couplers downward to the right height.
Remove the coupler lug from the car body. Scrape the paint off the coupler pocket.
Cut off the back end off the Accumate draftgear box.
Fit the .030 thick piece of styrene to the coupler box.
Drill and tap the piece of styrene for the coupler.
File the mounting screw flush with the styrene face. Glue the styrene piece to car body with liquid styrene cement. I use MEK because it bonds instantly when fresh. Coat both sides liberally and let the styrene melt slightly before shoving the coupler into the box.
The coupler should line up with a KD gauge. I had one coach that did and one that was low. Use Kadee washers to raise lower cars.
I use a triangular file to ream Kadee washers to fit the Roundhouse posts. Spin the washer on the file.
The draftgear has to be relieved to allow enough coupler movement on 18" radii. I cut the boxes back about a 1/16" with a razor blade. Make sure there is no ridge and the coupler swings all the way. It is easier to slice away the engineering plastic than filing.