Tman this is the cap I use on my Cuda. I use the windshield washer reservoir as the overflow. I did have to drill a small hole in the reservoir to keep it from vapor locking. After adding the vent hole which is in the rear of the tank under the hood pin support it has worked perfectly for 7 years.

Some people will say you don’t need the hole but when I added the overflow I also added a new thermostat which I checked on the stove to see what temp it opened so I could see where it was on the gauge so I had the cap off and when it opened checked gauge. Then when I put the cap on it statered to get hot. Opened lid on tank to add coolant and it started to flow fine closed lid vapor locked again. Lol

So added vent hole and never looked back.

Mike