Engine Swap Mounts - You might need to get a different k-member because these say they are for 67-72 K-members.
@manzysol Is your 73 a V8 or /6 car? I would trade you a /6 K-frame from a '71 for a 73 V8 k-frame.
Also, I have a 73 Space Duster 340. I have sub-frame connectors because there are no braces behind the seat like in fixed seat cars. I'd recommend them for you too being that you are going with a big block transplant.