Body Mounts. The parts manual shows three different “spacers” or more accurately, washers (Fig. 196. Items 6 & 11), used underneath the lower body mount cushions.
Of these, there are several NSNs. For the Front LH side, it is 5310-01-476-9321 , which also carries P/N 12339248-3. The Front RH and the rear use 5310-01-252-7285  (12339248-2). The intermediate mounts (the ones in the middle) call out 5365-01-214-4987 [5365012144987 5583215].
Other than the front left hand side (the most difficult mount to deal with because it bottoms onto the frame and can only handle a maximum diameter washer), we can find no reason for use of different washers at the different locations.
First, it is unclear what purpose these washers serve. We speculate that it is either to 1) spread the load across the metal portion of the lower mount; or 2) (in event of catastrophic mount failure), it would prevent the body from separating from the frame. There could also be some other reason we simply don’t know, but we have never seen washers used in this way for automotive purposes.
To be clear, we are not discussing the spacers used between the body and the upper mount to provide armor clearance on later versions.
After ordering all of the proper washers, two were on backorder status and we were only able to obtain two washers used for the front LH application, 12339248-3. (We like to keep extra parts in stock). This washer measured out at 5/8″ x 2 3/4″ x .250″.
Having only the LH washer/spacers, they measured at 5/8″ x 2 3/4″ x .250. The front LH definitely has a clearance issue, as that is the single mount with a “bucket” welded over the frame.
Comparing this washer to the lower months, it still covers the bulk of the metal on the largest mount, the intermediate mount 5342-01-186-7236  (12339247-3).
Upon determining that the smaller diameter washer appears to also work in the other positions, and being unable to timely source the washers/spacers called out for the right front, intermediate and rear positions, we determined that a washer of 3″ diameter will both fit and service properly.
We will use the extra front LH washer in the front RH location, and ordered four 5/8″ x 3″ x .250″ washers to be plasma-cut by my brother, David Grundman. As the washer 5310-01-476-9321  we do have appears to be galvanized, we will be powder coating the plasma-cut washers for corrosion protection.
We will update this posting should we find any issues with using the washers in the positions as described above. If anyone has any insight as to why different washers are utilized, we would appreciate hearing from you.