67 383 K Frame

I do remember seeing that bolt boss on the front of the block being used with some of the original mounts. I like your plan. If I had a original bb k I am sure I would use it also.
I have started a second spool type bb k- frame for a new project and this time around I started by completely removing the complete mount pads. I left the steering box mount.
I believe I can get a better fit by doing this. This started out as a 68 small block frame.
I will likely use poly inserts in the engine brackets.