Your new cranks are probably going to require a shorter BB spindle.
The new BB/spindle should make the distance from the inside of the chainring to the center of the seattube about 47.5mm. Trying the crank on your old spindle and doing the math to calculate what you need may be the easiest way to go.
And yes, loose bearings in the BB are fine. just use lots of grease to hold them in there properly when assembling. I'm pretty sure you're going to have to buy a new one though.