rotary

i just bought a kaaz differential and gears for my rear and i was wondering the difficulty level in changing it. and if anyone knows how to do it can you explain a little bit. if it is realy hard i will just get someone to do it but i think i might be able to do it. i do all the work on my car, including a clutch, radiator rear replacment
(housing and stock diff), motor mount and oil pan gasket. u know things like that. a mechanic said it is realy hard and if i dont do it right i will blow it up. i just want to make sure b4 i spen 400 on it.