ok guys needing some help and advice, first of all i need a six speed conversion for my car, and am led to believe i can use a v1/v2 ra rear diff and shafts is this true???

secondly what would happen if your box and diff had different ratios? what would happen? as i'm getting virations at high revs

not sure if its the diff or prop, i know its not the box. if it is the diff i cant use it in my other car for the 6 speed conversion