I have used a heavy duty 3 legged stand for a large variety of engines for decades now and never found it dangerous or unstable. It has the advantage of not tripping over the legs as you work on the engine. Personally, I would never switch to a 4 legged one. My engines spend a lot of time on the stand for cleaning, disassembly, running all the threads, cleaning oil and water passages prior to hot tanking, etc. Then again during assembly and painting. For me, rental charges would exceed purchase price. If you only need it once buy it and resell it. I think a bigger issue than 3 or 4 legs is the quality and strength of the mounts and how the mount is secured to the rest of the stand. The ability to easily rotate the engine is an important feature. 6 (or 8) cylinder in-line engines put more stress on this part than a similar weight V8. Its all about leverage.
Chuck
