I’m having a hard time getting to the motor mounts that attach to the frame, not the engine. Can someone share how they got them loose. What size is the nut? 3/4’’ ? It looks like the are adjustable, in a slotted hole. Mine are all the way down on the slot making it hard the get a socket on it. A deep well socket is too long and a short socket, the bolt bottoms out before it gets on the nut. I have even tried a swivel extension. At a loss now. Oh by the way the engine is out off the car.
I use a wrench and go from the bottom.
The Motor mount attaches to the frame via a 3/4"-20 hex nut, 3/4" split lock washer and a very thick flat washer that is about 1/4" thick and 1 1/2" wide as seen in the picture below. If you have the original flat and lock washer and nut on yours, there should not be a need for a deep socket. If missing washers and maybe using a jam nut you may need something a bit deeper socket but I don't remember ever having to use one.
So, with a large nut like this you want to use the larger 1/2" Drive ratchet, extension, U joint, and nut. Even if you can find a 5/16" Drive 3/4" socket you want to leave it in the tool box.. and if using 5/16" tools that might be a reason your socket will not reach the nut as they are usually shorter than the 1/2" Drive sockets.
With that here is my process from probably the last 50 of 58 parts cars: Raise front or front corner of car a bit & turn steering wheel so front wheel is turned out to give easy access under the frame area where motor mount goes through. I use a 1/2 Drive ratchet, 1 foot extension bar, U Joint, & 3/4" socket, attached in that order. I'm sure you know the old trick of wrapping electrical tape around the U joint so it doesn't flop around.
Again, I never remember having an issue with that large nut, once I figured out the right tools to use. When I remove an engine I always disconnect the motor mount from the frame via that one large nut, since after doing it so many times it is almost always about a 5 minute removal per side.
If you are missing the thick washer, or lock washer and even perhaps the nut I do have all the correct, original hardware cad plated as seen below. You an see more pictures and details by Clicking Here.