[1968 nova ss]

Guys, lookin for some help in painting the undercarriage and firewall on my other 68 nova ss in the black semi gloss look, some like it a bit flatter ,but a prefer a little shiny look... lookin for a mixing formula to achieve this look..currently the underneath is in a PPG DP 90.. it is ready to spray and would like to make sure I get it close...any help appreciated...PM me if would prefer to sent a mixing formula ,would prefer a PPG mix as this is a PPG store here in florida locally... thanks,Chris Teed