These models were originally built and detailed when all there was in the hobby of any quality was Athearn plastic F units. They have limitations, of course, including the wrongly shaped windshield openings on the A unit, and a much-too-flat roof contour, along with crudely rendered details and trucks (no longer true of the “Genesis” F units Athearn acquired from Highliners). But as I say, at one time they were pretty much the only game in town. In those days, I decided to model what railfans call the F3-Phase IV, meaning side panels like the succeeding model, F7, but roof details like an F3, specifically the rectangular roof slots through which centrifugal blowers pushed out hot air from the dynamic brakes. [I would not dream of doing this much work on an old Athearn shell today!]
The view below is at Rowen, on the north slope of Tehachapi, and it shows enough of the roof of both the leading A and B units that the dynamic brake slots are evident (Southern Pacific photo N-1640-13). The photo dates to 1948, when the units were brand new. You can click on the image to enlarge it.
On my models, I smoothed off the appropriate roof panels, including the steam generator parts on the rear hatch (SP did not own any F7-A units with steam generators), and cut slots for the dynamic brake openings. The slots were filled with screen. I drilled out the exhaust stacks so they would be open, installed diaphragms, and added lift rings as needed, plus railings above the cab windows. The result was like this.
The B unit roof was done the same way. On the A unit, I added all needed grabs on the nose area, installed headlight lenses, and represented a somewhat dirty windshield with wipers by the simple expedient of cutting a masking tape shape like the wiper path, putting it on the windows, then overspraying with Dullcote. Wipers are wire.
A side view of the unit shows another feature I thought was worthwhile with the old Athearn F-unit: creating flush window glazing, because the old Athearn body molding is so thick.
I did this by making a punch tool from 7/32-inch OD brass tubing, and filing the inside of the tube until the circumference just matched the outer part of the window opening on the Athearn unit. I then used the punch to cut discs from clear plastic, filed the edges smooth, and attached them to the unit with canopy glue.
One other feature I wanted to try and reproduce was the hoses between units. These are not very obvious in most photos, but in some views they can be seen. This detail from a Wilbur Whittaker photo shows what I mean. I discussed this point in my modeling column in the SPH&TS magazine Trainline, issue 45 (like most back issues, still available from the Society; see http://www.sphtsstore.org/servlet/the-Trainline-back-issues/s/41/Categories ).
My modeling approach for this was to make wire loops to attach to the B unit, with glue thickening at the loop bottom to represent connectors. When the two units are coupled, the wire appears to join to the A unit, but the units can negotiate tight curves or switchwork without interference between units.
The models then looked like this when on the track. Note that, despite my efforts to reduce it, the inter-unit spacing is still pretty large compared to the prototype. The diaphragms do help fill the gap.
As I said, the old Athearn F unit bodies have really too flat a roof contour, but as long as I keep these Athearn A and B units together, and don’t try to mix and match them with more accurate models, it really isn’t obvious in a passing train. But although my other Athearn F units are Genesis, I still respect these old campaigners.