IMO, if you're not looking to build a track terror, then springing for a forged short blocks is kind of a waste of money IMO. The stock short block internals will carry you into the 450hp range.
Your easiest and least expensive route to your goals is going to be a PI engine swap, with a blower. For $5,000, or slightly more, you'll have a running, high-11/low-12-second reliable Mustang put together with minimal downtime.
I suggested the Explorer engine earlier, because it utilizes the same H/C/I top end as the '01-up GT Mustang and also gives you the benefit of the 70lb weight loss of an aluminum block. Also, wrecking yards tend to jack up the cost when they hear the word "Mustang", but engines out of Explorers, Crown Vics, Marquis, etc tend to fly under the radar.
That should leave you plenty left over to get into one of the popular supercharger kits by
Vortech, Kenne Bell, ATI, Tork Teck, etc. This will be plenty of project for you and your son and it won't take you until he graduates from school to complete and pay for it.
I went the forged short block/custom route on my last car and it took me well over a year and a lot more than $5,000 to get together....and that was doing all of the work myself. In the end, I lost my shirt when I sold the car.
We've all got big aspirations for our projects, but take it from some of us that have already been there....the juice isn't worth the squeeze sometimes. Besides...even if you can't shake this forged short block thing, you'll always have your old engine on standby, ready to build up at anytime. That way you can take your time with it and still enjoy your car in the mean time. Remember....a car is worth nothing if it's not being driven. Don't end up like one of these guys
http://www.stangnet.com/mustang-forums/threads/anybody-else-experiencing-project-burnout.867004/ because your ambition got your further than you skill set, or budget or patience level allowed you to.