Rope length for replacing valve springs.

Good day everyone. I made a post a few weeks ago about valve sizes and valve springs. Welp the time has come that I'm ready to tackle the job. I'm planning to do the nylon rope trick and was wondering what's the consensus on length of rope to use? I don't have access to an air compressor.... . Thanks in advance for the help. Oh and the engine is a 360 with X heads on it.