You can not just buy a set of bearings and slap them in. You must as said above, mic the crank, mic the inside bore diameter of the rods and main bearing housing hole to fiqure what size bearing you need. The crank may need machining to adjust the size to make a proper oil clearance.
Here is a general guide I typed up a while ago;
I am not going to say any specific measurements, but this is the way to do it by math and not by plastic gauge. If you don't have the proper measuring devices, take the parts to some one who does. You need to be accurate to 4 decimals so dial calipers will not work.
1) Remove the crank from the block and take it to the crank shaft shop. Have it fluxed to check for cracks. If its ok then have it checked for straightness. I do this by placing the crank in a brass cradle and turning the crank by hand with a dial indicator on one of the center mains. All cranks will be bent to some degree. If it is more than .0013 then it needs to be straightened. This can be done in a press, by grinding, or by peening. I like grinding. If the snout needs welding, then forget checking for straightness as it will bend when welding.
2) If the crank is straight enough, then have the mains measured and compare to stock spec. If the mains are still in spec and are in good shape then the mains may only need a polish. Not too much or you will lose your oil clearence. Don't polish or grind at this point yet.
3) Install a set of main beaings std size into the block and main caps, then torque down your fasteners they same way as if installing. You must use the same hardware you are using in the final assembly. Measure the inside bore of the main bearing opening. This is done with I.D mics, then the mic is placed in a special holder and then you measure it with a set of micrometers.
4) take the measurement of the ID of the main brg housing hole and subtract the measurement you had from the crank. Ths is your oil clearence. You must do this for each main. Adjust the oil clearence to the desired amount by grinding and/or polishing the crank mains.
5) repeat the steps above for the rods and the rod journals. Rods must be checked for roundness first, if not then they need resized. Install the bearings and torque the cap down. Measure the ID, measure the rod journal, do the math and adjust the rod journals as needed.
Each rod must be kept with its rod journal, each main cap and bearing must stay with its crank main. Once measured you can not move rods or bearings around to other holes. You must keep them in order. Treat the job like you are sizing seven different mains and 6 different rods, not one crank as a hole. You may end up with different amounts of material removed from each main and rod.
