hi i am currently rebuilding a 302 cleveland the crank was stuffed so i got another one off ebay a while back but am just now doing it i was just wondering how do u find out the bearing sizes for it?

also i am modifying it mildly ,open plane inlet ,extractors, 650 dp carb will go bigger latter if needed and cam but not sure what cam to go with or wut to get it grinded to? will i get much more hps doing this? from stock

I hope you got a 351 crank for it?

Do you need some 351 rods at all?

get a 351 crank and new pistons
measure bearing journals with mics or verniers
id suggest going the whole hog and balancing rotating assembly and machining crank and bore
and replace cam bearings

GO ON DO IT
DO IT
DO IT
DO IT

Good idea but you forgot to mention you either need the heads too, or combustion cambers in the 302 heads opened up, or dished pistons as the compression ratio ends up way to high.

There is pistons available for using 302 rods with a 351 crank, but I have no idea if there is dished versions available, other wise you would need either the combustion chambers opened up or 351 heads. 302C rods will give more top end torque and less piston/bore wear.

in theory less wear , in reality more , i will never do a 351 with 6inch rods again and i know a few others that wont either due to massive amounts of piston/bore wear in short term

351 with 302 heads is about 11 to 1 which is fine with a good ignition system and premium fuel , ive never had mine ping anyway and it has a bit higher comp