Well it's good to hear that you aren't locked into the Jeep swap.
The LSC rearend will work but the swap might be more trouble than it's worth, you'll need to get out your tape measure first and compare the two rear axles to see how close they are in width. Assuming the width is close enough to work without cutting axle tubes & buying custom shafts then you'll have to cut off the coil spring/air bag mounts and weld on a set of standard leaf pads (if you carefully grind off the welds from the 9" under there now you can use those otherwise you'll need to buy or fabricate a set since most junkyards won't go thru the hassle of cutting a pair off for you.) Chances are the cheapest & easiest route will be to do exactly what S Bolt said & convert the existing rearend. I'd also convert the front to disks and once again follow S Bolt's advise and swap master cylinders because as he said the manual MC is *not* going to cut it and if you go thru the hassle of swapping to disks then you may as well set yourself up to actually USE them and swap in either a vacuum or hydro boosted master cylinder.
The C6 is a great transmission, it's hard to find anything more rugged & dependable. However, if you're looking to use this primarily as a daily driver then I'd really go with an AOD instead. From a design & engineering standpoint the AOD is the next generation C6. It's basically the same transmission with an overdrive gear added. Unlike the E4OD or AOD-E it's a purely mechanical tranny so it doesn't need a computer to shift correctly, it will work just fine in an EB installation and it's no more difficult to install than a C6. As a daily driver that 4th gear will make a huge difference in your milage and since I don't see fuel prices going down anytime soon I'd really suggest going with an overdrive transmission.
Nobody makes an EFI retro kit for a Cleveland, they're simply too old & too different and there just aren't enough of them since it was only produced for 70' to 74'. If that IS a Cleveland then the next best thing I can suggest would be to retro a Throttle Body Injection system onto it. Something like a Holley Projection system.
http://www.holley.com/502-20S.asp They come in both 2bbl & 4bbl configurations and give you the reliability, performance & milage improvements that most people are looking for in an EFI system. There really isn't anything out there for MultiPort EFI, even from the aftermarket vendors because the Cleveland market is so small. It seems like the only real MultiPort work being done is spearheaded by the guys in the Pantera crowd and those guys are pretty much casting up their own one-off intakes. I have a great interest in machinework & casting so I found it *very* interesting, just to get an idea of what's involved in setting up your 351C for multiport take a look at this:
http://www.bacomatic.org/irefi/irefi.html Maybe now you can see why it would just be easier to go with the Projection ?
Back to the Cleveland/Windsor question. Ignoring for a moment that you would need custom fabricated motor mounts & modified frame brackets here's another diffrence between the Cleveland & Windsor (and truth be told the Cleveland is really not all that it's hyped up to be, from an engineering standpoint the Windsor is far & away the better engine): Windsor valve covers use 6 bolts and Clevelands use 8. If you DO have a Cleveland in there do everything you can to take care of it since parts are getting *really* scarce and when you can find them expect to pay top dollar, don't bitch about the price just be glad someone had the part.
Just as a bit of trivia, the # of bolts on the valve covers is a good, quick way to ck what type of engine you have:
2 bolts the engine is a: 239/256/272/292/312 (produced from 1954 to 1964)
5 bolts the engine is a: 332/352/360/361/390/391/406/410/427/428/ (FE engine)
6 bolts the engine is a: 221/260/289/302/351W
7 bolts the engine is a: 429/460
8 bolts the engine is a: 351C/351M/400
and as another trivia tidbit the 351M/400 engines were the next design generation of the 351C.