I think most of the points have been covered above,
I agree, the price sounds awfully cheap for the 215A unit?
The factory 215A unit is a physically larger unit, size comparison
that's the reason for the longer bolts,
the charge stud is physically larger then the 130A, so using the oe harness, that's why the ring terminal has to be enlarged,
the belt needs to be 1/2" longer for the 215A.
I am not sure on the e-series, but on the f's the early years there was an alt bracket for the 130A and the 215A, the later years all used the 215A bracket. So either alt would fit on the later years.
The alt harness is different in that it has a larger charge wire and fuse holder, it is a mini harness that has the wire connections for the a/c compressor in the same loom, but those wires do not directly connect to the alt harness, the 3 wire plug is the same on either harenss. If you were to split the loom and replace the charge wire with the larger one from the 215A harness it would have the same result.
These are pics from my 215A install
Now, the link in the second post is a completly different situtation. That unit uses the smaller casing with the armature rewound to produce more current. So there would be NO modifications necessary, just swap units.
I have had that done before, (on other vehicles) and have mixed results. The failure rate seems higher in high stress situtations (such as limos) basically you are doubling the output but using the same casing to try and keep it cool. Sometimes though a physically larger unit just won't fit, so it is an easy alternative.