You can get a Fox .45 engine new or even used (if not terribly abused) for a good price (older ones tend to go fairly cheap on Ebay even new). Then get a head from DDD for it.
If you like OS engines the OS FP or LA series work well. DDD was selling a new OS 46LA diesel on Ebay, it might still be there too.
The larger diesel engines tend to be set and forget on the adjustments and much less finicky than the really small diesel engines.
My Fox .45 runs great as a diesel too. Plus I don't have to fiddle with the settings after it is dialed in. The needle is maybe a twice a year thing to tweak when the weather changes.