Other Rectifier tubes Alternative for 5AR4

I have several components that it explicitly stated that I can use a variety of rectifiers in the same family: 5AR4, 5U4, 5Y4, 5Y3 ... etc.

i have a custom built 300B power amp based on the Luxman MQ-300. It uses 5AR4, but it doesn’t state I can put in other tubes. How safe is it to put in other rectifier tubes mentioned above?

Thanks in advance.
It’s not an issue in this case since you have directly heated cathodes, but the 5AR4 also has a controlled warmup time to prevent cathode stripping. At any rate there aren't any good subs for it.
Do you mean my amp which is based on the Luxman MQ-300 is directly heated cathodes, so, I need to use 5AR4 where it has a controlled warm up?  And I can’t use a 5R4 because it doesn’t have the controlled warm up?
No. I mean that in your amp that quality won't make a difference. Cathode stripping is a phenomena of indirectly heated power tubes. Your power tubes are directly heated (the filament is the cathode literally) so cathode stripping is impossible.
Late to this thread. Just today, I spoke with the authorized Luxman warranty tech, Mike Garry, about replacing the 5AR4 with a 5UG4 in the MQ-300. He said do not do it. The amp's huge power supplies have an inrush that could be too much for a 5UG4. Or something like that. Glad I asked because I just bought an MQ-300 and I have a stash of nice 5UG4 that I would have tried in it.

Can it be confirmed that the LS100 will accommodate a coke bottle 5u4g in height inside the unit?