I expect to be able to place it on Assembling floor, but I cannot. (and also cannot place anywhere else)

Ah, that might be due to the space age surface restriction settings (where it can only be placed on certain planets by default)

I'll take a look at Warp Drive Machine, don't think I've ever used that one

I like it way more than warptorio, also updated for space age so...

Sorry for taking so long to get around to this, but I couldn't reproduce the issue; tested with just Warp Drive Machine v1.5.3 (and its dependencies), and Reverse Factory v9.2.1 (current latest), both with and without Space Age enabled.

It places just fine on every floor that I tested (except for the H floor, but I don't think anything is supposed to be placeable on that floor?)