I’m have a few Modern Marx prototypes-shop samples. Marx was very good about identifying these. I have passed on a few due to no markings or tag. Our forum friend Robert Butler has tons. Here are a few of my recent arrivals.
I love this one. Royal Canadian, I don’t think it was ever produced.
Marx Trains would begin fit checking as parts were being made, often using original Marx parts while waiting for their parts to be made. This was a learning opportunity for them to verify fit as their parts became available. This one is a fully functioning Modern Marx loco, but it has original Marx side plates.
Not sure about this one. The boiler is obviously a 8401 Marlines Loco, but the side boards are from the very hard to find gray PRR 8271. No factory markings or tag, so no 100% sure this is a factory piece. Due to the uncertainty, I've passed on a few others with no markings, but this one caught my fancy so I bought it anyway.