if this engine has been deck a lot and the heads to the block will get short and the dist will need to be check. there is some room on the oil pump drive but i have seen this if you bottom the oil drive it will push on the gears in the pump and tear the bottom of the pump and you will have a hard time keeping the dist from moving. do not shim it till you know were the dist gear is setting with the cam gear. check it the way i told you. there is no short cuts. if this is a dart block the dist will not sit in rigth the block needs to be trimed the back on 8wall hit the dist bore and will keep the dist up if you shim up to much you will lose the oil pump drive and burn the engine up from no oil and yes i have seen this to