I think Id go for a race meeting with USGT and LMP running separately and have a couple of the "classics" as special events: a 1.2 hour enduro (in the style of the 12 hours of Sebring) and a 2.4 hour event (in the style of Daytona and/or LeMans) where the two would have a "super main" where the classes run together. The separate mains would be as nrtv suggested (2 man teams, 15 minute mains with mandatory driver change...both drivers run at least 1/3 cume race distance to count for points, etc.)