Blazer suspension swap, 1977

[General23cmp]

I just purchased a 1971 K5 Blazer project, and the guy said he swapped the front and rear suspension with a 1977. I cannot see where anything was modified, but if I read correctly, this suspension/springs would not have bolted right in (maybe different length springs or widths…not sure). I cannot get back in touch with him easily. What options are there to do such a swap so I can get a better idea of what he did here? Would old springs bolt in, and then it be bolt in? Would perches have to be moved, and if so, which ones and which direction?

It looks factory as best I can tell, but I know it’s not. Thanks.