I have my 75 in place where I want it but it's not level length wise, do I literally just stick your average wood shim to make it level? And sticking a shim on one end wouldn't that make the middle loose contact with the floor?
Actually shimmed my 180g stand with cedar wood shims and after 18 years just scrapped the stand but currently have the same 180g setup on built stand never leaked. So for a 75 definitely yes, they do sell shims made of plastic some members have mentioned in other threads.
I also use regular wood shims on all my tank stands, most tanks being 100gals and up.
The house i lived in was built in 1870ish, so all the floors were off. I had shims stacked 3 high in some places.