shimano bottom bracket 68/70mm question - can you help?

[ti_pin_man]

So I need a slightly longer bottom bracket in my funk as the cranks are too close to the raised chainstays for comfort. Its the recommended 107mm axle length for the cranks, syncros alu ones. Looking for a un91/71 and theres a few 70mm shell ones around but the shell is a 68 I think but I vaguely recall that you can still fit a 70mm shell in, it just sticks out a couple of mm. Right? Its been a while since I installed any BB's. and I don't want to shop for the wrong thing.