sheepie

hi all this is my first post here anyway i have a major problem i am rebuilding a 125dtr that has been through the wars anyway i bought a new engine for it and didnt get a cdi unit or loom. The engine is a 3bn O3 plate from what i can tell and i cant tell what cdi unit i need as it is an old frame so cant use vin number what do i do? will any 125dtr cdi unit work? also i have no wiring loom i was planning on doing it myself but the wiring diagrams in the manual dont show how to wire pick up on magneto in. The bike will be for field at mo so just needs to go dosnt need lights etc any help please project cant go anywhere and i have spent so long getting this far and £££