Walt is right on and may have saved your engine!
The space (yellow arrow) shouldn’t be there. You need the later
idler arms for use with these tensioners.
Save your “mechanical tensioners. You can modify them to work
with the later idler arms by thinning the boss (use your new
pressure-fed tensioners to transfer the measurements. The
mechanicals are useful when setting the cam timing and of
course as emergency spares, (you need to deal with the oil
plumbing so the cams don’t get starved for oil).
Best,
Grady