Thanks ! Thats what it measured with calipers. 4.125" Must be stock, makes sense. Looks like someone pulled this engine from a Catalina or Executive (1968) and put it in the bird. They did put a Holley Street Dominator intake, and double pumper Holley carb, along with headers (and believe to have a new cam in it). Other than that though, it would appear they left the rest stock. Probably was standard protocol for pimpin a car out in the 70's, along with N50's and wheel flares. No shag carpet on this one though !