These are only suitable for easy, convenient biasing purposes, when installing trim-pots that can be adjusted without opening an amp’s chassis, and are good enough for that.
Your test points for stuff like 600V HT are already there - on the valve-bases, transformer terminations, and rectifier board.
Leave them there.
Important.
We don’t say “probes” in the industry. It is “probe”.
Never, ever work with two hands inside (or outside) an amplifier, unless it is unplugged from the mains, and has had it’s capacitors grounded.
For a ‘live’ amp, clamp one test-point probe single-handed, then test-probe elsewhere at will, keeping the other hand and your body always well away from the amp’s chassis.