Yep zahn cup for viscosities. There is a table to reference. Hydrometers(some come with thermometer built it) is a density tool. Which most things are then related to specific gravity. There is a wiz-wheel for getting temperature corrected results.
I was think there might be a correlation between specific gravity and BTUs. Then check viscosities would be helpful too. Got a project that requires higher quality and control then for the deuce. Just for consistency of the end product with mixing up batches. Especially with BTUs.
Some other questions is how does mixing gas vs diesel effect the flash point, autoignition temps, viscosities, etc. Knowing that cetane and octane are very different characteristics. I know BTUs can be calculated.