Can rusty cylinder heads be used?

so you need 340 block, right? Should be able to find one thats not covered in rust. I have built some 4"x 3" engines before and they are fun. Figuring out a cam will be a challenge for street driver. If you run a roller, the 340 has issues with lots of roller lifters as the lifter bores are often too short for rollers longer length. I still wouldnt screw with rusty block though.