What headers will work for a 87 5.0 HO

[Busamike]

I was looking around and I think the header tubes of the existing manifolds are too small. What headers will work on the 87 5.0 HO engine? I'm am new here and the more I dig the more questions I am coming up with on the car. Thanks, Mike

[spdbrake]

I take it you have flipped (R-L swapped) stock cast iron manifold's installed, and have J-pipes to connect the side pipes. Factory five still sell the J-pipes for the MK1 cars but not the shorty headers. I'd call them to find the correct brand that will fit. There are several thread with folks having fitment issues with BBK, Ford Racing and others.
some examples: https://www.ffcars.com/threads/ford-...itting.248813/
https://www.ffcars.com/threads/corre...-a-302.301640/

Its not the engine that is the issue, just accessories, motor mounts etc...

[MKS427]

FFR? GP Headers is who I used. There are plenty others out there. Gordon Levy, Mike Forte, and Gas-N come to mind. Did you check the manufacturers section?