I bought a bikenashbar steel mtb frame and fork from eBay. I needed a new crank and bb for it so I bought a king earl crank. now I'm shopping for a bb and found out the only one that works w/ those cranks is the TruVativ Howitzer. I found the 68mm that I need now i just need to find out if i need a 51 or 56 chain line. my intent is to run a single speed so I imagine spacing wont be in issue. I just want to make sure the chain ring wont rub the chain stay. this is the CRANK SET i got BONTRAGER KING EARL 36/24T 175MM ROCK GUARD BLACK. hope thats enough info. i guess my main Q is . is the 56 chain line bb going to be longer then the 51