It took me a few hours but I got it working!
Fixes needed
Replace all "/" filepaths with "\" (wrote a Python script to automatically do this for all gsc files - can share if others will benefit)
bsm_main.gsc - change line 48 to the below (remove parenthesis around GetPlayerAngles() )
angles = (0, self GetPlayerAngles()[1] + 90, 0);
bsm_transit_weapons.gsc - remove duplicate include line:
#include maps\mp\zombies_zm_weapons;
bsm_transit_main.gsc - comment out the below line 63 due to unrecognised "player" variable. I think this means that placing the hatch will likely crash/cause issues but at least it compiles! Will check later to see what the correct variable should be
player maps\mp\zombies_zm_buildables::track_placed_buildables( "dinerhatch" );
Diner is now playable! Thanks for your help!