Unless the car is in really bad shapre I wouldn't dip it. As long as you let it sit up a few days before painting, then a couple more after primer (just in case you get weeping), there shouldn't be a problem. The "ospho" is an acid neutralizer which should take care of that problem, but a thorough washing should fix it.
I'd be very cautious about dipping a unit body car. The oldsters don't have many enclosed areas, unit bodies do. If you do dip a unit body, make sure you tilt it a few hours to one side, the other, and end to end. The big problem is you strip off any factory corrosion inhibiters that were used INSIDE the various boxed sections, like the rockers. Those are major supports for the car. You'll need to get a rust proofing kit with long wands and drill a few extra holes so you can get into all those areas, or take it down to a Ziebart location. They drill access holes to enclosed areas too. The holes don't take away strength (hey, it's just a couple 3/4"-1" holes!, and they pop plastic plugs in just like the factory access holes. Now if you could get it dipped in primer afterwards that would be great, but no one offers that service!