the fit has always been a little loose, which is why im beginning to believe its that after changing out flange and collector gaskets multiple times on the drivers side.
as far as mods to fit the 4 speed:
you have to HEAVILY notch the passengers side of the lakewood bellhousing and block plate to clear the header. you also have to bend or move the lower leg of the z-bar to be able to get it to a full range of motion. also, if i remember right, you have to install the z-bar and linkage while youre installing the header. it seems like i remember not being able to get it in afterwards.
michael