The trucks in question, by all appearances, were manufactured by ASF. They were prevalent on the "Railwhale" 6-axle oversize tank cars of the 1960's, of which MCPX 23020 is an example.
There are lots of photos of the various cars at this Railwhales website.
Here is a press photo from ASF showing a new truck.
I presume you are within striking distance of the Pennsylvania Railroad Museum in Strasburg. They roster the PRR 500001, which features the ASF trucks. Perhaps a field trip is in order.
You may want to try and track down Bobby Pitts, aka "Tankcarsrule". He's an HO modeler with a thing for tank cars, and he's scratchbuilt really nice models of any number of them, including the one you want to build. He has had a presence on any number of forums over the years, I think he has a facebook page (can't confirm, I don't do facebook), and I know that he has a Flickr site. He may be willing to share information on either the prototype cars or his model build.
He has modeled MCPX 23034, with Buckeye trucks. It appears from the the Railwhales MCPX page that some of the cars received the Buckeye trucks later in life, with MCPX 23034 sporting Buckeyes in a photo captioned "Wyoming 1987". I have no idea if MCPX 23020 ever received the Buckeye trucks. I also don't know if you have your heart set on modeling 23020 specifically. But depending on your modeling date, you may be able to legitimately model a different car number with the more readily available Buckeye trucks. But where would be the challenge in that? 
As far as drawings of either the cars or the trucks are concerned, you might see if you can get your hands on a 1966 or 1974 edition of the The Car and Locomotive Cyclopedia. Various editions can often be found at your local library, or made available by inter-library loan. There's no way to know if the trucks are in either edition, without getting a hold of one and leafing through it. I can tell you that the ASF trucks do not appear in the 1980 edition, although drawings of the 11'-0" wheelbase Buckeye trucks do. I can always get you a copy of the drawing, which you could pull into cad and trace. The N&W Historical Society also has a nice drawing of a Buckeye 6-wheel truck, but I can't tell what the wheelbase is from the low-res image on their website. It can be purchased in electronic format, which is ideal to pull into cad. Their scan will be better than anything I can get out of the cyclopedia, but then you get what you pay for I guess. 
By the way, that reminds me of something. If you do decide to go with the Buckeye trucks, be aware that there were different wheelbase length 6-wheel trucks made by Buckeye. So the PSC or Wiseman trucks may not be appropriate even though they are Buckeyes. If I recall correctly, Bobby Pitts indicated at some point that he had to scratchbuild the correct 6-wheel Buckeye trucks he used on his model, which he did based on the 1980 cyclopedia drawing, because the correct wheelbase was not commercially available.
Hope all this helps, and good luck!
Jim
