Because people asked for it, here's my arm and door modification [for Human Alliance Jazz]!

The arm and door modifications I made are not terribly hard to do, but there is some careful planning involved to get the best fit. I'll start with the arms which came from Alternator Skids

I happened to have an unmodified Skids in my collection so here's a before-and-after view:

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I ground[ed down] the outsides of the forearms down some to get a more rounded/less beefed up look. Then, I filed in a new line to keep some of the character. The important part is the upper arm, though, as that's what fits into the Jazz figure. You have to cut very close to the screw holes but not into them.

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I don't have another HA Jazz for comparison, but the red lines on the two above show what needs to be cut away to make the parts fit cleanly. You can see in the second picture that the white outer part of the shoulder (the under part in the picture) sticks out further than the black inner part. This helps to keep the fittings straight and hold everything in line.

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Snap, click, [and] everything is flush and tight and straight - so much so that if you do it just right (without any glue or screws or anything), you can do this without fear:

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TA-DAA!

The doors are much simpler, but you do still need to be careful:

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I ground[ed down] and sanded everything, but the hinge down on the inside of the door to make room for the arm in car mod. Then I used some Milli-put to attach a post (I used LEGO pieces, but whatever) at a small angle:

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Here you see the bigger circle shows the two screw posts you need to keep intact; the inner circle is the area you need to fit your drill bit into. On the right is what it looks like assembled:

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There's not a lot of room in there but there is enough you just gotta get the angles right and your posts sized correctly.

Here is the finished result:

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