Factory tolerances on these cars was loose at best. It is not uncommon to see some critical dimensions that vary by .125. If either of your mounts is 1/8" off, you have a windage tray to drop the pan further, and an engine mount pedestal is off an 1/8", now everything will rub.
I'd recommend you check dimensions as provided by Brad's diagram. If you need to move the idler down, then file or grind like shown, and weld an oversized washer into place to lock the location down.
Another possible/additional solution is to shim the engine mounts up .125 to lift the engine up a bit.