Thanks Gus -
Good idea to check the Stovebolt Tech Tips - don't know why I had not done so.
The '54 Shop Manual says that the upper plate and lower retainer may need dressing to provide 3/64" to 5/64" clearance between the two. The Shop Manual also notes that if the clearance is more than 5/64", a new lower retainer must be installed. Yeah, right -- I'll just run down to my local Chevy dealer parts department and buy one! ha
EDIT - That is a great write up about the front motor mount. My thanks to Don "down2sea" McLendon for writing it and to you for linking to it.