Early FH engine, Piston differences to a FB/FD Pistons

I dont have my manual to hand and dont even know if it has the answers but, i have an 1471cc FH block and as part of a future rebuild plan i have found some FB /FD Nos pistons but im unsure apart from a slightly different part number what the differences are? They appear to be the same bore but i cant find anything else.

Any help would be great

Mark

So the two pistons have the same part number but the fh engine has S on the end of the part number and the FD/FB engine has a R on the end of the part number..


So basically does anyone know the difference between R and S marked pistons as i think this is the same across lots of engine of the time.

Cheers

Mark

Think i have it, i think the S ones are dished on the top and the R are flat - there may be other differences however....?