eperry: I am also in Boise. I'm afraid that I can't find any definitive information regarding a 350 swap. There is a lot of vague info out there.... have you found anything on the net?
Therer's not much out there with much detail that's very specifc to 55s. There is a member on this board that used a Marks adapter (Australian product) for his conversion, he goes by Mtrdud, you can search his posts to see what he did. The Marks adapter is expensive...~$1100, but it allows you to keep the toyoya tnans and transfer case in the stiock position, while still giving you firewall clearance with the V8. So not a bad way to go if you are set on keeping your Toy 4spd tranny.
As others have mentioned, there's alot of options, just really depends on what you want to do with it, and what you can afford these days. After some deliberation, I've decided to go the used 5.3 vortec route and use the GM auto trans with it. For what I want, a durable family truckster to load up and take fishing, camping, hunting, rafting, etc., I like the mileage I can get from this fuel-injected setup, and while I may not be set up for any heavy wheeling, it will be plenty capable to get me where I need to go.
I've checked at Barger Mattsen here in town, and you can pick up an "A" grade 2000 and later 5.3 vortec (mileage under 60k, or less thah 10k per year), with the transmission, harness, ecm, all engine accessories for ~2500. My plan is to find one of those I like, freshen it up as necessary, and get started. AA and Downey both make adapters to mate the GM 4l60e to the toyota transfer case, and then there's other details to work out of course...Front driveshaft clearing the transmission oil pan (There's a modified output shaft and flange for this, see BTB products), rear crossmember for the transfer case (AA makes one specifically for the 55, works like the standard 40 rear crossmembers, bolts on to the transfer case).
In a perfect world, I would put a 5speed NV4500 manual in...But they are considerable more expensive than the 4l60e, so I decided to just keep the auto most of the vortecs come with.
My $.02...Good luck! I hope to see you on the road here in Boise.