I looked into all the things you have mentioned. You can install another engine from another manufacturer but all the work would be custom and cost around the same $5000 or more. There are no mount kits for swaps or aftermarket plates to line the tranny up. The wiring would be a another issue along with the computer system. This is uncharted territory and you'd be the first to make a path should you choose it. I bailed on the idea because I didn't have the time to invest in the research and design. If my motor would have failed in the spring or summer I might have went that road because I could ride my motorcycle all summer. I needed the VX back so I could go to work in the snow and wintery weather.
I searched online to find an engine for cheaper than I could buy from the dealer but could not find any. I don't trust a used motor from a junk yard so I had to make a decision and just go with it. I don't regret my decision to have the dealership install the new engine. I have my VX back and it runs great. Also I now have a 2 year 24,000 mile warranty on the motor, that is if Isuzu would really back it should something go wrong. That's a whole different issue I'll have to deal with when and if the time comes.
I look forward to hearing ideas from others here about this.