My case was similar. I had to do some cutting/ welding repairs on the ex-racebike frame so the motor was already out and the frame was bare. The bike was a parts bike that I had for 10 years and was disassembled partially never thinking it would ever see the road again, so I never heard the motor run properly. It had stock CV's with no airbox so I heard it pop and sputter a bit before taking it apart, but I wanted to hear it idle before I started investing a lot of time on the motor. I had other motors I could put together if I had to. I sold the carbs at some point and was going to modify the intakes to use slide carbs. I knew there would be some testing I was going to need to do and the frame was nowhere near ready.
I made the stand as a wheel barrow so I could wheel the motor around in the basement. One single rod goes through the motor mounts at the lower front portion of the engine. This allow me to tip the motor forward to access the bottom. I put a metal pan on it to catch drips etc. That was handy. I could change the oil by using a shallow pan. To make the motor level, I just let ithe rear end rest on a block of wood.
For inline fours, the engine will be stable during acceleration, but deceleration might might try to tip it forward so you have to lock the back end down. I just used that bungie you see in the photos. It was more than enough and the motor seemed very stable.
I made the stand from wood re-claimed from other projects so the whole thing came together pretty quickly. I had a lot of the hardware from other deck projects etc. Probably took a couple hours to assemble, and maybe another hour or two to shape the pan and main rod holder. Most of the metal parts are the framework of wheels for cabinets etc. I pulled them out of the dumpster at work, but you can find other substitutes for that.
It was much nicer doing work without the frame around the motor for cleaning gasket material etc. on the clutch cover and valve cover. I also had to fix some parts on the trans cover. Access for cleaning the grease buildup was very nice.
Now that the project is over, it has become the defacto battery maintenance area, plus it holds a bunch of other junk too.
I had a post with the use-whatever-I-have build, but I think the photos are gone now.