BTW, PDP-11 (and PDP-8?) uses 74 logic chips, not discrete transistors, so I would say it's already complex enough for tubes.
Going the opposite direction I always wanted to reimplement the flipchip modules using SMD technology just for fun. A discrete transistor SMD PDP8 that fits on a desk would superficially seem realistic, at least for a large enough desk. Honestly I just don't want to pay for the connectors and wire the backplane connectors. The SMD components could turn 60s era "handheld" flipchip modules into postage stamps, but no technological progress has happened for wire wrapped backplanes so my SMD design's backplane would remain exactly the same size and complication as the original -8, unfortunately. I'd have a giant tangle of wire wrap wires and a couple hundred postage stamp size "nano-flipchips". Probably 50 pounds of interconnect copper and 1 pound of circuit boards, LOL.
This is whats likely to get Op. Its easy to make an adder or a latch, but takes an entire spool of wire to connect one up to the overall circuit. Lots of work.
Sure, if you use 1950s germanium transistors, RTL and DTL logic is no fun anymore. I always wanted to try RTL and DTL using something more fun, like 2010s era microwave low power amplifier FETs. I would not like to pay for it, but it would be a lot of fun to build a 50 GHz ALU or similar. I have no idea what I'd do with it other than say "wow" a lot, which makes it an ideal hobby experiment.