Lacquer thinner can be used and is effective but you must use a clean damp cloth and wipe it gingerly. Don't let it stand or get wet or it will quickly soften the existing paint. If you have pre sanded the entire car with 320, then a lacquer rubdown and tack ragging should get you ready for a coat of sealer followed by color/clear coats.
I use MEK (Methyl Ethyl Ketone), it leaves no residue and will not dissolve any paint except for laquer (including uncatylyzed primers!). It's cheap like borsch and evaporates like alcohol (good ventilation!). Most chemical supply houses will have it. Here's an <a href="http://www.temarry.com/MSDS/Methyl_Ethyl_Ketone_msds.htm" target="_blank">MSDS</a> on it's properties and safety/health concerns.