Welcome to the Rail Wire!
The WOT RTR cars are very nice and very accurate in regards to the SP. You mentioned the 60' cars, he previously released a 70' Baggage (ex El Paso & Southwestern) cars. The latest being the 80-BH-1 "Baggage Horse" car. Again, all very accurate regardless of the SP paint scheme. You were wondering about the early resin "kits". Here's a short list of SP releases:
Stock # Car Class Finish
WOT #102 70' Baggage 70-B "Dark Olive"
WOT #103 70' Baggage 70-B "Dark Lark Gray"
WOT 70' Bag-Postal 70-BP-30 "Dark Olive"
WOT #122 69' Bag-Postal 69-BP-30 "Undec"
WOT #118 70' Baggage 70-B-8 "Undec" (Streamlined Heavyweight for Lark)
WOT #119 60' Postal 60-P "Undec" (Streamlined Heavyweight for Lark)
These cars are very accurate as well. You just have to build them.
Hope this answers some questions....
