Scarpia, there are also 4-wheel NWSL power trucks, see:
http://www.nwsl.com/Catalog/pg019-cat4-03-v0605.pdfhttp://www.nwsl.com/Catalog/pg020-cat4-04-v0605.pdfThe catch with using them is that the minimum wheelbase is 7' in HO. The shortest wheelbase Black Beetle is 25.5mm, again, about 7' in HO.
I'm guessing that the Peckham trucks on the cars you want to model are shorter than that? If not then you could use either. If they are shorter, and you would like to model them accurately, then you need to consider an alternative power truck.
I'm not familiar with the cars you've posted the photo of*, but they appear to be a combine, in which case you could use something like the Hollywood Foundry truck. Install it at the end with freight compartment where it wouldn't be visible, and use a dummy truck under the passenger end.
Generally speaking, I don't bother with detailed interiors on my cars, I'm happy to use window shades/blinds etc to conceal the bits like motors and decoders I don't want seen.
The Proto87 page you linked is very interesting, yeah? I've been watching their announcements very closely!
Cheers,
Mark.
*What road did they run on?