ok, I had been meaning to rig this up on my old pickup, and if you want to do it with a 350, then here's some pointers/ideas that I had. I haven't done all of it because... 12mpg is bad enough and I can't really justify the addition of turbos. I just put fuel injection in it and a .440/.454 lift cam and this old 4x4 will hit 50 before you know whats goin on.
- get an older sbc. in the 70's to... 82 or 83ish they ran 8.2:1 compression, and then in about 85+ they ran with swirl heads at 8.5:1 compression. the swirls flowed a hair better than the 70's ones, but were very prone to detonation according to a performance shop I went to. one idea is get a 350 diesel and swap the heads for gasoline use, this was a common modification at dealers because the 350 diesel sucked giant hairy monkey nuts. you'll have the stronger bottom end, but I don't know if you'd have to swap pistons. The biggest problem with the 70's heads is the middle two bolts going to the intake manifold are at difrent angles depending on the years. Thankfully the fuel injection manifolds are aluminum and God invented dremels.
- install a high flow oil pump. they really ARE high flow oil pumps, not just ones that SAY high flow. you can physically compare them. my 1978 pickup's oil pressure is about 45psi at IDLE. 75psi allllll dayyyyyy lonnnnnng.
- ram's horn manifolds. you'll recognize them if you see them, they're very squat. you simply flip them upside down (yeah they'll still bolt up just fine) and rig some kind of adapter from the exhaust of the manifold to the turbo. a nice chunk of plate steel should do. this should be easier, cheaper, and stronger than building custom headers.
- fuel injection. my fuel injection came from a 1990 gmc van. the ecu in a van is under the driver's seat btw. just rip the entire intake system and the spark timing mechanism. don't forget the knock sensor thats down on the right side of the block. it goes into a drain hole for the water jacket so sbc's already have that hole tapped. I have a 78 model for crying out loud. My ecu is laying on a rag on the left wheel well and is none the worse for wear. The stock fuel circuit uses the oil pressure sensor as a switch for the fuel pump, and without that oil pressure sensor the fuel system will cut out after a bit. I use a switch on the dash. Rigging the hookup for the turbo to the tbi may be difficult however, and keep in mind that the stock fuel pressure was a mere 14psi. you'll have to figure out some kind of rising rate regulator. The stock regulator is adjustable with a philips screwdriver (do a search on google for how) but I don't know if it will raise fuel pressure to compensate for boost like ours will. Oh, and don't forget the fuel pump.
- oil lines T'd off of the oil pressure sensor line in the back (behind the dist) and and T the coolant off the heater lines. you want the turbos to be below the level of the radiator so when they sit there and boil the coolant off, the steam can go into the radiator and not just sit there. the return lines for the oil can go into the oil pan. I was planning on using twin mitsu's and putting a cone air filter on the intake of each turbo. have them sticking up there like horns. Maybe a flap in the hood (vaccuum operated or manual, I hadn't really decided. be neat to be able to do it in car in case it started raining) to open up the intakes on some bullnose hood scoops to feed those turbos.
Hope this helps. Most of that is probably useful no matter what engine you use. I just felt that since the engine probably couldn't survive 13psi (its almost 30yrs old), and my K engine did that stock it just felt useless to go to all that trouble if you're not going to be able to run good boost.
TurboDodge.com 
