One of the worst enemies to these old Mustangs is rust. My first response would be the unpainted one because new paint hasn't covered up the rust yet. If it is relatively rust free, the paint shop can repair any small rust spots. But, if the floor pan is rusted through, that will be expensive. So, check it over for rust damage. I paid about $5,000 for my paint job, but one half of one of the rear quarter panels need replacing, and I went ahead and had the windshield, headliner and all the rubber replaced. There are paint jobs, and then there are paint jobs. Don't take it to Maaco. You may get by with a $3,000 paint job though. Look the car over carefully. How does the interior look? That's a$500 or $600 job if you do it yourself, and it is a relatively easy job.
To help tighten up the front end, get a Monte Carlo bar and an export brace on the engine bay. Depending on how loose that suspension is, you may have to replace the suspension. I recommend a Grab-A-Track replacement suspension. Get a new set of KYB shock absorbers, and don't drive 100 miles an hour in these old beasts. They weren't dynamically designed to go that fast.
If a manual transmission is what you are looking for, then seriously consider the manual tranny car. A swap from automatic to manual is quite expensive and very time consuming.
Later on down the road you might want to consider putting on Disk brakes on the front, followed up by a dual bowl master cylinder. The dual bowl can be bought at just about any auto supply store, and is a fairly easy swap. Ask for a 1967 model. Remember, safety comes first , so get it safe before worrying about paint, etc.
Any more questions, chime right in.