Your opinions on these jackets?

[HeathBar]

So, assuming that a casual kilt is worn at the traditional kilt placement (waist, not hips) and has the same fell length, is there any reason a jacket wouldn't look 'right' with it?

No. My above comments were geared towards "low riding" casual kilts. Sorry for the confusion.

[piperdbh]

I like #2 and #4 the best.

I'm in the middle of doing such a conversion job, and I'd advise this: figure out what kind of cuffs you want on the sleeves (gauntlet/Braemar/none at all) before you cut the length off the jacket. You'll need to measure carefully if you want gaunlet cuffs.
Regarding the pockets: if they're not patch pockets, you might be left with a sewed-up place where the pocket used to be, with a really cool flap covering it, like I have on one of my jackets.

[MacMillan of Rathdown]

All of them will convert into excellent kilt jackets, with or without epaulets or "traditional" cuffs. The trend nowdays seems to be away from "Highland" cuffs, unless the jacket is cut from a traditional tweed, so you might want to follow fashion and save yourself the trouble of doing all of the extra tailoring.

[Squeaky McMurdo]

#2 looks the most like tweed to me, but they're all nice.