I have a set of Rear coilovers from a 510 from techno toy tuning that i did not use on my 510.. i would like to use them on my b120 somehow, has anyone done this and how did they go about it. 4 link? 1 leaf? how did it come out. Obviously i would like to go about it the easiest way.. but if i have to get a 4 link it is an option.

I used coilovers and 4linked my 1200 sedan but it isn't the easiest thing and there's a lot of cutting/welding to get it in especially if the car sits low

Remove the existing shocks and bolt in the coilover shocks. Remove the extra three leaves from the spring pack, but keep the main leaf to locate the axle.

The 510 upper shock mount is a bayonet type, while the B120 ute is a ring type. So some modification is needed there. The bottom of the shock is the same.

Would the removing all the leafs make the rear axle sloppy? also what would be the easiest way to change to the ring top on coilovers

the axel locates itself on the leaf pack just fine, there is a locating hole\pin for that purpose

im looking at doing the same thing.. does anyone know of any coilover's that would fit in place of orignal shock..

Yes, SPAX and PARADISE sell them. See Coilovers, section "Rear"