so you have a 68×111 that "threaded in fine". i assume that you mean you were able to reassemble the bottom bracket, tighten the adjustable cup/lockring properly and have a nice, smooth-turning spindle with no side-to-side or up-and-down play. okay. now you want to attach a pair of cranks to this spindle, correct? have you tried the cranks that came with the bike orginally? dafydd is correct that trial and error is an inevitable part of what you are trying to do.
the only reason i can think of for not using the cranks you already have is that you cannot physically put them on the spindle. the perfect combination of cranks/spindle is not a matter of life and death; there are things you can do with the rear wheel to improve your chainline. in fact, i can guarantee your rear wheel will need some fussing with. if the cranks you have are totally useless, find another cheap set somewhere, preferably from a bike someone is throwing away. this is the essence of "do it yourself". good luck!