First a few observations about O scale Gem PRR models - over the years I've owned the models below.
A5s 0-4-0 - Made in Japan in early to mid 1970's. Reasonably well made, open frame motor, but dimensionally inaccurate in drivers, boiler diameter, and length. Perhaps a phantasy PRR A6s. IMO the best PRR A5s to date is the one built by Samhongsa and imported by Weaver - well made, good runner, and for detail hounds a great starting point for upgrades details (e.g. tender foot boards), and corrections (pilot height).
B6sb 0-6-0 - Made in Japan in early to mid 1970's. Reasonably well made, open frame motor, dimensionally correct drivers, boiler diameter, and length.
B6sb 0-6-0 - made in Korea in late 1970's early 80's. Dimensions common with Japanese Gem B6sb, Pittman can motor, some improved castings, but spotty workmanship and low quality metric machine screws. O scale 2 rail alternatives include the well built Williams/Samhongsa B6sb (late model short cab, reverse slant cylinders. As with the Weaver A5 a good candidate for up detailing. Precision Scale Co. imported B6sb's from Korea in several versions. They were finely detailed but note that the "long cab" version cab length was short of scale length - disappointing given the price of the model. Frank Miller retrofitted the cab on my PSC B6sb with one hand punched by Steve Grabowski's dad- many thanks..
F3c 2-6-0 - made in Korea close to the time of their Korean B6sb. To the best of my knowledge this is the only model of a PRR Locomotive that predates the 1920's standard era PRR front end look. Assembly was cleaner than on the Korean Gem B6sb but can't comment on the running qualities as I only ran it on a test track. I sold it soon there after as I focused my PRR layout and rolling stock roster on the 1950's.
Perhaps my favorite small PRR steam locomotive is the D16sb. In addition to the 1223 preserved at The Pennsylvania State RR Museum (and operated under lease for many years by the Strasburg RR) , two D16sb's survived in lease service on the Delmarva peninsula Baltimore & Eastern RR branch line until 1950. In the early 1960's Max Gray imported a model of the D16sb built in Japan by Toby. The Fall 1964 MG Customer Service Bulletin had a photo of the model with a $139.50 price. They may be among the hardest to find O scale model of a PRR prototype. Earlier this year I was lucky to win a near mint MG D16 (less tender) on-line at a surprisingly low price. The closest to prototype tender I could find was a body off a Gem F3c. It will require re-detailing as the firing deck of the D16 was lower than the F3c. Thanks to CLW tender truck side frames from Lou Houlemarde and machining by Ed Bommer the tender now rides on proper trucks. Other project list items include upgraded castings, turned down flanges, ball bearing NWSL gearbox, can motor, and DCC/sound. The D16sb project will be several years down the line as priority I is to signal the railroad. I'll be using the NMRA's Layout Command Control (LCC) bus architecture and logic boards from RR-CirKits) to drive more than 40 PRR position light block and interlocking signals - more on a later post. Meanwhile I smile when passing the D16 in the display case.