they fit a factory v8 monza bellhousing.
here is a picture of a factory v8 bellhousing
viewtopic.php?f=1&t=36168
on the off chance that you have a car that was converted to mechanical clutch linkage with a bellhousing that has the clutch fork aligned horizontally the 2135 headers can be made to work by cutting out the bend in the #7 pipe and welding in a straight section. It would be simpler to get the correct bellhousing though.