I replaced the original tailgate latches with gas struts on my EK wagon as I only had one working latch, and the little clicky locks were painful to use routinely. I did some measuring using this as a guide:
I took that to one of the local truck spare parts places. They sell gas struts, and can fill them to whatever pressure you need. I measured the tailgate weight using a "hanging fisherman's scale", divided the weight by two and that's the weight they were filled to hold. My tailgate can be lifted up by hand, and stays wherever I put it... it doesn't go pssssht and raise up on it's own, which is OK by me.
A word from the wise... I had images of driving around with the front windows open and the tailgate upper lifted. It's raucous (I like raucous

) and dangerously fumey. Won't be doing that again.
Mine bolts into the existing tailgate bolt holes on both the window and frame side. I moved the strut ends around using some steel brake tube offcuts as spacers. I used simple bolts rather than the ball-end ones you see on modern cars... they work OK, but there is a slight sideways load that the ball-end would take care of. Hasn't failed in 12 years of daily use though

- Wagon upper tailgate struts top mount.jpg (542.23 KiB) Viewed 693 times

- Wagon upper tailgate struts bottom mount.jpg (450.54 KiB) Viewed 693 times
Cheers,
Harv
327 Chev EK wagon, original EK ute for Number 1 Daughter, an FB sedan meth monster project and a BB/MD grey motored FED.