kscarbel2

The part number for a B-81 radiator cap is 16MF24P2.
The part number for the rubber gasket (not included with the cap) is 104AX63.

Okay, so based on the stamping, your truck's front axle mounting arrangement is 1QH39315P5 (that's a 5-digit Mack Western type arrangement number), and the model is, as we've already mentioned, FAW5371C (FAW537 series, 12,000lb/5,443kg).
Mackpro, what was the number of the 1QH arrangement you saw, when looking up RWS721LS-1528 ?
From your pictures, this appears to be a single rail chassis. Some bridge formula mixer chassis ran single rails because the mixer body acted, to an extent, as a supporting subframe. But my experience was we had crossmember failures and frame rail failures. Your truck has a far deeper frame rail than an R-model, but I question the long-term durability of this truck in tipper service when articulating off road. As I mentioned earlier, a (self-steering) pusher axle could help two-fold.

Allison automatics were a factory option on the MR, R, RB, RD6, RD8, U, DM, RWI Super-Liner and MH Ultra-Liner.
Allison's MT654CR, HT740D, HT740RS, HT750DR and HT754CR could be paired with the E6-270, E6-275, E6-300 and E6-350, or Cummins NTC350/Formula 350, NTC365/Formula 365 and NTC400/Formula 400.
And the Allison MT643 was available behind the Caterpillar 3208 in DM492 and MR492 chassis for municipal and government orders.

On the left side of your Mack transmission, toward the rear of the main box case, is the stamped identification information.
1. Mack transmission model number
2. Serial number
3. 11KBA assembly number
4. P number, which designates the variation of the main assembly.
The 11KBA number is used together with the P variation. As in this example, 11KBA51478P1. This is the number Mack dealers use for looking up your desired replacement parts.
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Also probably no longer available, but Mack interior trim supplier Belmor (vendor code 7909) was offering thru Mack dealers complete interior trim kits in Levels 1, 2, 3 and 4 (http://www.bigmacktrucks.com/index.php?/topic/34169-mack-cabs/).
Belmor also offered the new style 1984-on interior design in beige color for older cabs. It was a sharp looking installation, a major upgrade over the old (pre-1984) beige "deluxe interior" option. I recall it being available with a full-size headliner, or a partial headliner (shorter in the front) intended for the installation of a (beige) overhead radio console.
http://belmor.com/index.html
Now, I did a quick search and came up with this seller for the 1984-on beige kit:
http://www.finditparts.com/t/300/manufacturer/mack//products/2604217/mack-204sx130