340 engine mounts

The 318 mount is wider than a 340 mount, so that would mean the 318 tabs are wider.
Some have used a 318 mount on a 340 motor, by making up the difference with washers.
Kind of a hokey way to do it if you ask me.

If your drivers side mount is wider than your 340 tabs it is from a 318.

The biscuit mount holes are the same on A-body's.

This is where it gets tricky, because E-body 340 mounts are different than
A-body. I have seen people trying to pass E-body mounts off as A-body.