I can't speak to the 2x4, but on my 3x2 air cleaner, the hold down holes are 10" apart. Also, the air cleaner is shifted to the front: From the back hole to the back (firewall) end of the air cleaner is 6 1/4". From the front hole to the front of the air cleaner is 5 1/4". Figure if someone has an unidentified lid, this may help determine what it fits.
Pat