Mark,
DDL is a PPG lacquer product. I don't believe they make it anymore. A number of states prohibit sales of it (commercial/industrial use).....VoC regs.
Pretty much anything you can do in an enamel or lacquer you can do in a urethane. PPG's high end urethane line is Deltron. DCC is their single stage urethane product, DBC is their two stage (used with a clear coat) product. Some colors, like metallics are only found in the DBC line. Urethane is a better product-I have 25 year old restorations that the paint looks like it was done last week.
There are additives to control the degree of gloss you want...ie: gloss, semi-gloss, satin, flat etc . Those are just a name, you control the actual degree. Texture also.
TCP is a distributor. PPG has their own color library and people. PPG has an auto refinish web site.
What you might want to do is go talk to your local PPG jobber or a body shop that uses PPG products. Other paint mnfg's are organized the same.