The rough running could easily be a symptom of fouling from running WVO. Unless you're prepared to invest a lot of time and effort into properly treating and filtering the WVO and tearing down the injectors and wearing out injection pumps, sticking with diesel is the way to go. You have to be very meticulous in your maintenance and occasionally run the car on diesel fuel or a diesel/WVO blend, otherwise WVO is a death-wish for the engine.

Given that you can only use few parts off the car in question, the unibody is potentially damaged from collision or rust, and you can't fit comfortably in it anyway, the whole thing seems like a big ol' "Pass".

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)