273 302 318 340 build

Yes they normally have the small end bushings, for the floating pins which you indeed have from the description of the pin lock grooves in the pistons' pin bores. Sounds like you also have the package of 16 pin locks somewhere with the pistons.

These are the heavier SBM rods which were used in the 360's also and later found their way into the 318's, under a variety of casting PN's. The weight you showed for the rods is spot on for data found in several sources. I looked at all of your other weights and such and they mostly look normal; the piston compression height should be 1.841", and the difference between the pin diameter and the small end hole (the pin to pin bore clearance) should be less than .001" (i.e., it will be reeeealy snug) so those numbers may be off due to measurement accuracy.

I'd go with a rubber formed rear seal; MUCH easier to succeed with than the old rope type seal. (At least for me....)

Thanks for the eyebrow check.... numbers are always appreciated.