I'am in the process of replacing my flat top pistons with new take out pistons and I have run into a snag. There are no marks or notchs to indicate the front of the piston. On my flat tops there are notchs, but on the stock pistons I bought , there are just numbers and colored dots on top. On the pin boss on all of the pistons they have a R. Does that indicate REAR. Any help would be great.