No doubt stuffing a small block into your 4x4 will require serious suspension work. I have not actually tried this type of mod myself (the 350 in a t-truck) but have done a few others in the past. The motor mod itself will keep you busy for a while since there will be plenty adaption work. But nothing is impossible.
The weight change will definitely require that you beef up your suspension so your truck will handle properly. Being an older vehicle the suspension no doubt has some wear already so an upgrade to a stiffer suspension will give you the excuse to put in all new parts!. You already have the 3" min. lift that is required.
Is your truck a 5 sp manual? If so this will make the mod to a small block much easier as the 83 and newer 5 speeds came with a removable bell housing and there are kits available for this conversion.
As for the engine, well here is where the real work comes into play. I will give you a quick run down on the required mods that I know of.
1)Firewall conversion due to xtra length and distibutor location on the 350
2)front radiator & grill sheet metal area moved forward approx. 1 1/2" due to engine length.
You should have no problem fitting the engine between the toyota frame rail except the turbo mods. which require more lift. Just be sure that you end up with enough oil pan (for suspension travel) & distrubutor clearance when you stuff in your new small block.
I hope some of this helps! Good luck with your toyota mod and keep us all posted. I love to hear about the mod work on these puppys.

OH WHAT A FEELIN!!
*HERMIT* the T-Tech
Looking for a good rear chrome bumper for a 91 4x4 DLX Toyota pickup