By all means I am all for seeing this done! Do not take what is said as a deterrent to not do it!
With that said, for what you are doing, and respectably looking to double the power you have now, the 94 truck motor platform would be a low budget option to get there. It would take some work, a few tweaks here and there, and you would have a power limit with out making changes. But to literally shoe horn it in and go you would have less than a grand in the whole swap if you do the leg work to get the parts you need.
Now what I would suggest is get the truck, and see if someone would be willing to trade it for mid 90's mustang (preferably 95 gt manual trans). that way you would have everything you would need to do the swap without much money in it. It would have the proper ecu, engine platform, trans, etc. That would give you the best of both worlds, and still be what you originally intended.
As far as the jz swaps, its more money, but definitely a solid platform. The swap is quite popular in the 240 scene. They make specific kits for the 240 to bolt them right in, not sure about the bmw. But either swap would require custom brackets I would imagine. The benefits would warrant the cost, but it wouldn't be the nostalgic v8 growl or simplicity of a naturally aspirated 5.0L