between the frame rails it is 29" with the lip removed at the top of the rail, the core is approx 1/2 wider ( 1/4" per side) than the opening, that a is un cut core support opening and it was a origional slant 6 car if that makes a difference in the core support, the one I ordered was 555-52018, the info says Ford but it is Ford/Chrysler and also it has NO trans cooler built in but does have a bung for a drain petcock, I am building upper and lower mounts like I have done for the other one that was in the car I think side mounts could be made also.