There's some special airgun spring compressor however which I found just too costy and you can just use the normal clamp compressor to finish the same job.
It's good that you have them and pretty sure you know how to use that.
I followed the below video to do my HW35. The 35 is almost same like the 80, so you will need to know what's what that's good to start the job.
https://youtu.be/wrAbruYs_MUAnd there are so many similar videos on YouTube and they may give you different info regarding the job, go search 'HW80 tuning', 'break barrel strip down' etc etc on YouTube to find them. Better watch as many as you can before starts. And take pictures at every second moment you think you should keep a memory. This habit helps a lot.
You may also find the videos looks seldom show you a spring compressor!! However to me, I am not Hulk 100% at all, so I just can't finish the job without a compressor.
You need to know the strong spring is powerful (17fpe energy), at the 1/10 second the end cap (maybe 'end block') getting off the action tube, the spring will push everything apart. And then, when you putting back the things together, you need something to help you keep the end block and action tube stay together steadily, you can turn it to engage the treads... That's the time I need the compressor to help.
At the time you order your kit, you can also pick one or two backup piston seal which you don't use it here you must need one later and you don't need to look for where to buy when you need it in the future.