I was in a body shop once that did a lot of hotrod type work. They had a much larger version for working on car bodies.
OurWorkBench raises some very good points about the stresses on the stand. Your average sewing machine is going to be around 35 lbs. That's a pretty substantial amount of weight to hang off 2 pivot points. There will be additional live loads on the stand as you work on the machine too. The stand's construction needs to be solid. Any weaknesses will make themselves known quickly.
Rodney