This is my Onan 20kw Generator 20.0DL4-15R.
Engine Onan/Cummins L423D I 10198B Serial C843771372 (1984) RPM 1800 Timing 19 Lube Capacity 5.7L Injection Pump: Stanadyne Roosa Master DB2-4086 Model 4324495 Muffler Burgess-Manning silencer, BEO-2 1/2 (see brochure), Coding AP-4-34 P/N 52-168-0
Some links: Article on Roosa-Master DB2 pump, Stanadyne Roosa Master Manual PDF, YouTube video on Onan L23D engine (by yours truly), more pictures of L423D engine (by yours truly, from another project). Also you can see my older Onan DJE generator, which I since sold.