as far as i know even tubes can be placed in arbitrary position. from the way the amps were designed i've seen the elements placed onto the number of different positions with no compromise. on guitar amps many times you can see tubes placed upside-down. on high quality amps very often you can see tubes placed sidewise to save the space.
BUT
there are could be transformers and coupling elements that need to be placed right otherwise they might hum. the toroidal transformer and low-capacitance capacitors basically can be placed into any position while the large coupling capacitors, power and output transformers, coupling transformers need to be placed as mounted by manufacturer.
BUT
there are could be transformers and coupling elements that need to be placed right otherwise they might hum. the toroidal transformer and low-capacitance capacitors basically can be placed into any position while the large coupling capacitors, power and output transformers, coupling transformers need to be placed as mounted by manufacturer.