well ive stumbled upon a couple deals that are good but all have sm465s and ive always wondered how hard it would be to swap the T400 on my suburban to an 465. when i do all this itll be behind a 454 and in front of a 205. 99.9% of the time im out in the mud so if that makes any difference as to whether or not i should swap it lemme know.

im gonna take from the amazing amount of responses i have (lol) that this is probably a bad idea

Well I have a '85 burban and it was stick.... At the time it was a SM465/NP208 on 44" hawgs. I loved it in the mud, cause i had granny gear I could just ride all the mudholes in 2nd and when I got on it I could slam it in 3rd and let her eat at 4-6K all day long. The only reason I got rid of it was because I drove on the road most of the time and in rush hour traffic it was a pain in the ass...especially since the syncro's were messed up...so thats why I pulled it and they wanted 600 to rebuild it so I got a TH400 from a buddy for 150 bucks with a stage 2 shift kit and it did fine in the mud too but I didn't have that extra low gear for creeping...not sure how much of a difference in ratio it is, but it was noticable...
Since then I have upgraded my motor to a 468 BBC that puts out way more power then the 350 SBC I had in it and put 2.5ton under it and it's starting to slip now...so i'm thinking about switching back to the SM465 now...
So it basically boils down to preferance I supose...they both have there pros and cons...I'm sure eveyone else can fill you in on that..

If you do go stick, I'd put a performance clutch in it, I had a centerforce Dual-friction in mine, and about 30k road/ and prolly another 5K of hard in the mud rompin around on that clutch and when I pulled it, I could barely tell it was worn.

As for difficulty, If you run a hydralic clutch (like mine was) i say is should be fairly straight forward.....I don't know if all the provisions are there in the firewall already, so maybe a little drilling, but all you have to do is bolt your master cyliner to the fire wall, put your resivore above it, and run the shaft from the cyliner to the clutch (pedal should be a easy bolt in) and you will most likely need to change your brake pedle (or cut it) to fit the clutch next to it (autos came with a wider pedal). And you just run your line (looks similir to a brake line) to the slave cyliner and your done. You may need to get your drive shaft cut...or if your 205 is mated you have to get a differnt adapter and not sure if it will rest in the same location as where it is now...so you may need to trip your F & R shafts.
Now from my expierence with the hydralic clutch, "learn from my mistake" and use 600+ degree brake flud, and make a heat shield to block the heat from the exhaust. Other that, you should be good to go, if you choose that route. I'll see if I can dig up some pics of the heatshild I made and my set up.

added:
perf. Clutch about 250-275
throw out bering 30-35
slave cyliner 35
master cyliner 45
hydralic line 20
(those are what I would get new)

the pedal, trans, bell housing, resivore, fork i would get from a donor vehicle and the flywheel but I would get that surfaced...15-25 bucks depending on the machine shop. Use new bolts with this ARP is a good choice 25-35.
clutch kit will come with allignmet tool
oh and you'll need a piolt bering for the back of the crank 1-3 bucks.

LOTS of people have made that swap. Try here: http://coloradok5.com/auto2manual.shtml

that is exactly what i needed thank you to both of you guys. when my suburbans done ive got a 454(mayb a 496) goin in it and have found a couple rockwells for the setup so that is exactly what i needed to hear. thanks