For an R40_42 I'd go with 24.5-32 drive tires. I'd also paint them to match the combine they are on. We got new rear wheels for our 79 N6 that were silver (came off CaseIH) and the next year I painted them AC orange so now everything looks normal. I have an Uncle who kept his wider rear wheels off his l2 and put them on his green l3. I'm still trying to get him to get some silver paint. I know some may think it's no big deal, but if I was buying something used, I'd sure want it to look like it should.