My 82 started out as a straight six banger. I bought an 80 Capri with a 255 v8, and used the k member and several other trinkets, the throttle cable, etc. The 82 six had the same brakes as my 79 5.0, which were bigger than the 80, so I kept them.
You can adapt v8 mounts to the six k member, but it is much easier to just swap. 8 bolts.
The k member simply bolted in, the struts, steering, all fit. Note that in the 79-82 area, there are two types of steering shaft to rack input shaft adapters, one with a flat and one that is all splined. If you use the same rack, no prob.