I think for the sake of safety and ease of work, I will look for a quality compressor. The one the the guy uses in the video, a Proform brand, seems pretty good so I'll look for that one. Although the valve holder tool isn't expensive ($10 on Amazon), I definitely appreciate the tip on the clothes line.
Btw, are the diameters for the seals pretty much the same, or will it vary by motor? I tried looking them up on Summit and they have several different diameters for an SBC. The reason I am concerned is that this engine is a crate engine, so I am not sure if it would be the same as the one for a stock motor in a '77 Chevy.