I'm not at all familiar with PRRs truck class system... other than 2 is for number of axles and the letter is the AAR axle type.
All kinds of truck designs could be said to be manufactured in house, especially before the 1970s or so... when quite a few railroads had their own foundries and could easily cast sideframes and bolsters (and even cast and machine wheels and axles) to whatever design they needed (just look for the railroads initials on the sideframe, that's a dead giveaway it was cast 'in-house').
