Any reputable engine builder will tell you if the stock crank comes out you’re going to want to have the block align honed (or aligned bored if far enough out of spec.) The mains have been worn in with the stock main bearings. If you just throw new bearings in without mic’ing and align honing you could easily spin a bearing. With that being said it’s your motor and people do sloppy mechanic stuff all the time to save money. Just do so at your own risk. Also like the guys said above... if it aint broke dont fix it. Do a compression test, leak down test and look at oil pressure when warm. If everything looks good keep driving it till the wheels fall off unless building for more power or racing purposes.