So, in terms of N-scale equipment offered that'd fit for the dual 45' trailers would be the BLMA/Atlas F89Js and the Athearn F89F RTTXs, right?
In theory yes, but there's a couple of caveats though, depending on how accurate you want to be.
For me and for 1985, the most important thing is the TT logo - you don't want the TTX speed logo (1991), you want the older TT style with some brown flats amongst the yellow.
This limits your options for what BLMA/Atlas and Athearn have done so far. Even their announcements for future runs of those cars, for true Twin 45 flats, are only shown with the TTX logo.
Trailer Train's conversions to Twin 45s in the early 80s went STTX (with sliding bridge plates - TOFC only), then WTTX (portable bridge plates - TOFC only) and then TTWX (portable bridge plates, but all-purpose for TOFC/COFC) and then ultimately RTTXs for Twin 45 / Triple 28 service started in the 1985-87 period. In the early 1980s, the RTTX mark was still being used for open, tri-level autoracks and TTAX wasn't yet spine cars.
I don't have time for the full table, but V1 of "The TTX Story" has a table that compares the flat car fleet in 1973, 1983 and 2000, and here's the spread in 1983:
TTX - Two hitch TOFC (ie, 45' + 40') - 8,739 flush deck + 19,445 other (ie, standard level, raised sill) = 18,124
TTAX - TOFC/COFC all purpose (AP) - 13,665 flush deck + 0 other = 13,665
Others - presumably low deck TOFC flats = 4,369 total
WTTX - Twin 45 TOFC - 0 flush deck + 953 other = 953 total
TTWX - Twin 45 TOFC/COFC AP - 812 flush deck + 0 other = 812 total
STTX - Twin 45 TOFC - 366 flush + 384 other = 750 total
TTCX - COFC Only - 681 flush + 0 other = 681 total
XTTX - 4 hitch TOFC - 120 flush + 332 other = 452 total
KTTX (Twin 45), RTTX (Twin 45 / Triple 28) = 0
So on numbers alone for 1983, 95% of your Trailer Train fleet would be either TTX or TTAX reporting marks, with TT logos and two trailer hitches (45' + 40' slots), in the following car styles:
- ACF Flush Deck - MTL
- ACF Flush Deck - Atlas
- ACF F89J (raised sill) - BLMA / Atlas
- BSC F89F (raised sill) - Athearn
I'd still expect a mix of older brown TT flats amongst the yellow TT flats as well. The newer Twin 45 conversions came from former auto-racks, so they'd newly painted TT yellow.
For some variety, but the flush deck ACF flats could be used in COFC service as well - both Atlas and MTL have had this offering.
Currently, no one makes the 3rd most populous option - a low level TOFC flat developed for clearance under catenary (ie, LTTX flats).
For mind, the best way to achieve the Twin 45 variety for your 85 period would be any of the available options, changing the hitches to suit and re-decalling the reporting mark to suit STTX/WTTX/TTWX with the Microscale options. I'd have a single XTTX flat to round it out - but Athearn didn't do the four hitch variety properly (it's a standard TTX deck) and I'd have it as one of the TT brown cars.
