The opposed twin should be better balanced than the V twin, and is even-firing so it will sound better (like a BMW twin motorbike). I agree that the side valve engines may be less sensitive to precision in maintenance, but most of the large OHV ones have an oil filter, which is a plus. It seems to me the main issue is cost: if you can get a durable, reliable engine that is easy to maintain for not much money, that is a good deal.
Remember, you need that air cowl, or the engine is not worth buying. You can't operate it withtout the cowl, and I don't know where you would get one for a sensible price. I can't remember an opposed twin ever coming up on Outdoorking since I've been here, so they don't seem to be common in Australia, and that means the cowl may be rare and expensive.
The air cleaner is also missing in the photo. I don't know if you could get one of those or not - you probably could, but it will cost time and money.
I hope he hasn't been running it without the cowl and air cleaner.
