We are currently in the later stages of a similar build.Started out as an engine swap.62 Lancer w/440. You know what happened next. Purchased welded 4link subframe from A.R.T. as a focal point and built from there.
They offer a 10 point cage kit for a 69 valiant that I asked them to add a foot of length to all the legs. After trimming it fits great,main hoop,halo,and all.We already had CAP front a/arm components,so we just built a jig to incorporate the Lancer front end geometry into the new 2x3 frame rails w/coilovers and rack and pinion. We would have chosen a strut front end, inretrospect,but it started out as an engine swap.
Don't want to highjack your post, so we are going to try to post some pictures soon.IF we can help w/any info, you can pm me here. Good luck