Re: b18b crank = b20b Crank???
Yes the b18b and b20 cranks are the same, but if you install it all clearances must be checked. If the tolerances on the mains is to tight then yes it will need to be line honed. If you indeed had a rod bearing spin the once again the rod will need to be checked and resized or replaced. My advice is pull the block and get it to a good machine shop and go from there.