I took my crank to the machine shop for a polish. When the worker was examining the shaft he notice groves between the shafts where it suppose to be smooth and shiny. He statind i will need to grind the shaaft down to the next level. I already bought the standard size main and rod bearings for the engine im currently rebuilding and my question is can i use the same bearing i bought or will i have to down size them. If so, what size should i down size to?

This is an example of why never to purchase pistons or bearings until measurements are taken.

You want the machine shop to remove the least amount possible. Any competent machine shop should advise you what is needed. If possible, 0.010" cut and therefore you will need 0.010" oversize bearings.