There are some threads in the research forum that discuss thrust stands and measurement tools. Aerocon has a page with pictures that various people have sent in over the years as well. They show a simple one that's a 5 gallon bucket filled with concrete that has a metal I-Beam embedded in the concrete. The load cell is attached to that. They act like everyone has metal I-Beams just floating around the garage, but I sure don't.

I was considering using metal square tubing, something like you might use for a receiver hitch on a truck.
Mine are likely to be smaller, so at the moment I'm leaning toward 2x4 construction with some weight and tent stakes holding it down. The motor will point down, so keeping the unit in place is more about preventing it from tipping over than anything else.
I considered the HX711, I'm curious what your data looks like when you get some. I went with an Analog Devices eval board which has the ability to run the load cell and a pressure sensor. The down side is software sucks so I'm working on that as well. I was also wondering if I thought 80 samples/sec would be sufficient. For thrust it probably is, it might miss short pressure spikes though. With sugar, it might not be as important. It seems people usually run sugar motors at lower pressures anyway.
Be careful with PVC. If it goes, it makes plastic shrapnel, doesn't show up on X-rays.
You really need a LEUP for sugar motors? ppffftttt... How stupid.