Henry Bushkin — the former lawyer for Johnny Carson who penned a revealing tome about the “Tonight Show” host last year — is beginning rehearsals for a musical based on the book this week.

We hear that Bushkin’s pal, jazz man Steve Tyrell, is creating tunes for the show, and rehearsals will take place at Bushkin’s summer home in upstate Bedford.

Tyrell has just gotten back from London, where he performed at Prince Charles’ birthday bash.

Bushkin was spotted talking about the show on Thursday at Primola on the Upper East Side, where diners included former Yankees manager Joe Torre and slugger Tino Martinez as well as Marianne Nestor, widow of designer Oleg Cassini.