i recommend you get some pb blaster. soak them good for a few days. now these are which bolts? are they the ones that are integral to the rubber mounts? if so you can just buy new ones and drill them out if the pb doesnt work. or are they the ones that hold the air filter top on?
if they are the top ones i dont know how hard they will be to replace if you have to drill them out.
Diesel loving autocrossing grandpa Architect. 82 240d, 83 300TD with five speed, 03 Dodge 3/4 ton with cummins six speed; I have had about 33 benzes. I am building a 39 Studebaker Coupe Express pickup street rod at the moment in which I plan to install a 617 and a five speed manual.
....or a 64 stude v8.