The best thing to do is find a donor car from those years. I think the 79 to 1982 are pretty much the same. Your 79 is the first year for the new body style after the Mustang II thing. I had a 1982 Mercury Capri which was a Mustang body car and that had a V8 302 hipo. So find a Mustang V8 donor car one that maybe is wrecked or just in bad shape and use the cross members and drive line from that, this way you have all the same components needed to make the V6 to V8 swap. I have done this type of swap from a small blog to a big block in older Fords, it makes it a lot easier. You will still need to upgrade the suspension and brakes but the donor car can still have usable parts. I would check wrecking yards and look in your local paper for parts cars for sale. With time and patience it can be done.