Valve holder tool that goes in the spark plug hole

[JanGaLanG]

I use an Allen wrench.

 

[95 shaw]

Hmmm actually, you are correct. Do you have that other tool? I can't visualize how it works.

For even double springs, you can usually just use your hands for removal and installation.
Used with the hammer for 150# seat pressure springs for SBC.

 

[flattop1]

Wow . I trust ya . Austins keepers on a big twin was a two person wrestling match even with a spring compressor.

 

[CarlsonMotorsports]

Another thing you can try is to take a pair of long needle nose pliers and coat the tips in rubber. This way you can grab the valve stem through the port to hold it. Of course, this entails removing the exhaust and carb to access them, but it's another tool/method to keep in mind.
Back when the clones were just getting crazy with valve springs being replaced every night, we used shoe string down in the spark plug hole to fill the cylinder many nights at the track. Whether in tech or between races, stock 10.8 springs can be changed with very little effort. Heavier than that and I think you'll be looking for some better tools.