Thanks to Tarkus pointing me to memo's notes on the first Aspyr release, I have found the solution and have been able to update a few files on the LEX for MAC 64bit compatibility.
MAC versions of the game have always had an issue with Float32's that have a Rep Count of 1, but never this severe before. It was originally noticed with Transit Switch properties, preventing stations from functioning properly. Now the same issues are appearing with 3 Slope properties on lots, causing a CTD for 64bit MAC players.
There seems to be little rhyme or reason to what may be causing the problem, and it isn't an error I've been able to repeat with PIMX or SC4Tool.
But I do remain committed to helping as I can, regardless of the OS, so please report any problems with 64bit compatibility here, and I will try to provide a fix as soon as possible.