RE: D&RGW pipe gondolas, what are you using for pipe?
I just finished two pipe gon loads using 1/2" CPVC pipe from Lowes. Part number 23811, $2.07 for 5' (they have it in 10', but I didn't want to cut it in the store and 10' is too long for the car). It scales to 12" OD which is one of three sizes mentioned as D&RGW loads in my web reearch (along with 8" and 24"...the latter must have been culvert???). Evrything L found seemed to indicate the pipes were 40'. However, I cut mine to 42' since the Accucraft cars don't appear to couple as tightly as the prototypes so 40' looked too short (didn't lap the idler flats much. I added some blocking per the prototype to raise the loads so they'll swing clear over the idler decks. I've decided to use 15 pipes per load in a 6-5-4 truncated pyramid. Six pipes just fit side-to-side.
With respect to the Accucraft idler flats: as mentined by Accucraft and others, these were some of the first attempts and used cut down high-side gons of the same class as the pipe gons. However, they didn't all go away as there are a number of photos showing them in later years (and a few survive) with the deck-top reinforcing rail (15' according to Sloan). Pictures of very similar 9000-series gon-to-idler conversions also show a brake wheel lowered nearly to deck level. I've added the rail and lowered the barke staffs as I want to run these as gon-flat-gon strings. While I haven't found a phot that proves the brake staffs were lowered on any of the 1000-series gon-to-idler conversions, it works for me. last detail that I plan to add are some U-bolt stake attachments which Sloan (and some photos) indicate on some of these gon-to-idler conversions (and, specifically, for one of the 2 road numbers I have.
Last, must do detail IMHO is to add the deck overlays that Electric Model Works offers. One issue (which I'm bringing to Jonathan'a attention) is that the idler flats are longer than the standard flats for which the overlay kits are designed...you'll need 3 extra planks. So, either order one extra kit to provide the extra planks for a dozen+ conversions or perhaps jonathan will offer a somewhat larger set for the idler flats.