Any (small) Lego Technic parts not in whole units?
I assume you mean L when you say units?

Well anyhow, unless I'm misunderstanding, I would try these: https://www.bricklink.com/v2/catalog/catalogitem.page?P=6575

You can stack 3 of them up to get 1 and a half L

If you mean 3L long instead of 3L wide, this should still work because it has axle holes which is 1.5L apart, it also has axle holes that are 3L apart.

Search youtube/eurobricks for 'technic mini engine' / 'technic micro engine' for some ideas.