The PDP-11 was unusually well suited for that. They designed it so you needed less skilled workers to assemble it which meant a lot of tolerance in components which leads to much easier maintenance. For example, the backplane is wire wrapped so there's no soldiering there which can eventually tire out. If things move around, oh well.

Also the PDP-11 was designed at the time boundary of core vs semiconductor memory with the clear intent to be able switch to semiconductor which led to an unusually flexible design around memory (and also affected I/O design). Check this 1975 paper https://dl.acm.org/doi/pdf/10.1145/800110.803541