This is a custom hand-made water neck, which accepts a GM thermostat.
For the radiator cap, the options are as follows:
Mishimoto 2.0 Bar: This is a standard radiator cap, nothing special about it.
Meziere Radiator Cap: This one has a billet top, and is locking, so it cannot vibrate off ever. This is a super high quality radiator cap that looks amazing.
These are hand-made to order, and usually take about 2-4 weeks to ship.