Only the rubber fuel lines, maybe the fuel pump if it is an older one. Plus possibly any rubber seals in the carby if they aren't E10 compatible. I don't think it will do any internal damage, I used to run it is my WB tonner with a red 202 in it back in the late 80's-early 90's. Make sure it is a HT-HJ or blue 4.2L compression levels though as these are all 9:1. HX-HZ are 9.4:1 and might not like it. The difference is the pistons, the HX-HZ have a dome top, others are flat tops IIRC.