haha, I thought I was on my Jeep board. The LS swap is kind of popular with the FSJ crowd. Jeeps that look like this:
Both easier and more complicated in an old Jeep. Easier because some companies make things like engine mounts, more complicated because of the transfer case and front/rear drive shafts.
I keep talking myself out of it for the jeep. The expense just isn't worth it since the Jeep runs fine now and I just don't drive it much. An LS swap would allow me to easily run an OD transmission. I would also gain fuel injection (which is good for Jeeps that you take off road) and of course horse power.
But in the Jeep world when going off road reliability is key. The LS engine is reliable but all of the custom engineering to make it work isn't. Simple things like routing the wiring can cause issues. So at this time I am still keeping it simple. And it's kind of fun to run with the new rigs while sporting a 71 Jav engine and a carb.
So back to the question about the mustang. I wouldn't do it. Not because of any blasphamy but because of cost. I think there are other options that would keep the cost lower but give similar results.