Found some tidbits in some of the old threads for you:
"As far as cleaning, get some Mud Off (or something similar). You can get it from Speedway Motors or anywere that caters to dirt track racing. Mix it with water and spray it on every place that will build up mud (inside of fenders, grill, underside of trunk, etc.) It smells like something similar to WD40 and will keep mud from sticking as well. This stuff is pretty cheap and a bottle will last a while."
"Also, the Mud Off goes on the car before it goes onto the track and keeps the mud from sticking. Sorry if I made it sound like it was a cleaner. Make sure that you do not spray it on your harness inside the trunk area (if it has petroleum in it, it could hurt the nylon webbing). "
"We use a 50/50 mixture of baby oil and WD40 to keep the mud from sticking. Put it in your garden sprayer and get the insides of the fenders and the leading edges. "
"After some quick searches, I have also found that some are using cooking oil sprays (Pam, or the generic equivilent). Hit up your local Dollar Store and buy it by the case.
Also the baby oils and WD40 are very popular. Be careful with the WD40 as it may peel up your decals."
Usually;The local car wash will get the job done. Do be careful spraying around wiring and carbs. Filter covers, plastic bags, etc should help.
Steve