Just like with Andrew's Cougar mentioned above, you've got plenty of room in a '69 engine bay for an LS (without having to chop shock towers, like in an earlier Mustang). With that in mind, you're not likely to find a "kit" without doing something like a Mustang II crossmember--that's probably as "off the shelf" as you'll get.
If you really want it, be the guy who does the research (measurements/angles/bolt patterns), then tells the fab guy exactly what you want. It should be relatively simple. You've got some great fab guys local-ish to you, like DuSold and Vorshlag. Vorshlag puts LS engines in BMWs and Scions, so your Mustang (or just some applicable one-off parts) would be a piece of cake for them . . .
Oh, wait . . . there's a guy on Pro-Touring.com who did a '69 or '70 Mustang LS conversion with a Griggs Racing subframe, but that's not bolts, and you've already bought stuff . . .