I have this one on my 968 engine. I would talk to 928motorsport and see if it's compatible with early 944. IIRC they're all the same and they were used on the 928, 968, and even found their way onto the 986.
https://928motorsports.com/product/replacement-heater-valve/
I did have one of the plastic types split in half on me on a drive once on my 944 engine. Never again.