JBlast Supa, I think is the way to go, have used it several times with very good results.
Don't bother with Soda for blasting armour - too gentle, plus you need a special pot.
I use a large contractor style Hodge Clemco pot with a 2 tool compressor from Speedy, with good results.
Paint as soon as possible, definitely same day.
Don't use any iron based abrasives, because any you don't get out before painting will shake its way out onto your freshly painted surface when you start using the vehicle and rust.
Definitely use the proper air fed hood and put some ear plugs in too!
You should easily be able to blast and paint a 432 in a day. Post some pics and write up on how you get on so others can learn from it.
That's my two cents.
Good luck, Richard