Malcolm
As others have said, both the Lionel PS-4 flats and the 40 foot flats are very nice cars. They have diecast metal frames, so they are properly weighted, and they have real wood decks, which respond well to weathering, tie downs, etc; Because the cars are diecast, they have a lot of fine scale size details, like grab irons, drains, end stirrups, brake wheels, etc
The holes you see in the deck are to accommodate a “covered tarp load” that came with the car. They can easily be filled with wood putty before weathering the deck. The covered tarp load is not bad, but I like to “roll my own.:
(SORRY ABOUT THE DISTORTION IN THIS PHOTO!)
These are easy to convert to 2 rail, I glue the Kadee coupler box to the underside of the floor with Goo and Zap A gap. The 40 foot flat car above uses Lionel trucks, with NWSL wheel sets. I don’t do that any more. The PS-4 flat you see below uses Intermountain Trucks and wheel sets, and as a result is lowered properly. I also routinely fill in the slot at the end (that was originally there to accommodate the three rail coupler) and I weather the deck extensively.
I wrote an article in OST (#63) about turning these into PRR F30D TrucTrain flats. But many of the techniques apply to all the Lionel flats
Cheers!
John