I work at Arrow Engine. And its true, we have discontinued the Witte Diesel engines a few years ago. And we do not carry very many Witte diesel parts. The Witte diesel parts we do have are either left overs that just havent sold yet, or parts that interchange with the Witte E-20 gas engine.  The reason behind killing off the Diesel line was simply supply and demand, Arrow was only selling 3 or 4 unit per year and it just wasnt cost effective to have 100 sub bases, cyl heads, and blocks casted and mahcined just to set in storage. You will have better luck finding a witte diesel from a antique engine collector \ dealer, and you would get a cheaper price from a collector \ dealer rather than a oilfield engine rebuild shop. I have seen several over the years on
www.SmokStak.com for really affordable prices.  There is a common misconception about Arrow rebuilding engines, We are not in the bussiness of rebuilding single cyl engines, that would take away work from our customers. The only engines we rebuild are the 2 cyl gas engines, such as the L-series engines. Which are too big for most engine shops to handle anyway.  As for engines running on "home brew" fuels, I do know of one Arrow C-series engine and a few Fairbanks ZC engines that run on Wood Gas, essenitially these engines run on smoke. There more to it than that but you get the picture.