Gregg Allman's glory years will always reside within that brief period when his brother Duane's virtuosic guitar licks would effortlessly interplay between his own Southern blues vocals and keyboards. Making a single song last up to 40 minutes, the man behind such career-defining tunes as “Midnight Rider” and “Whipping Post” has never really lost his influential importance. Spanning his days as part of the Allman Brothers Band, to his solo work on albums such as “Laid Back” and “Playin' Up a Storm,” Allman is scheduled to perform a special reserve-seat show at the National with openers Scrapomatic at 7 p.m. on Friday, Jan. 8. $35. 612-1900.