You do realize that extending the boom you are dealing with more issues than just the legs not being long enough.
Depending on the material and construction of your extended boom, it may not be strong enough for the weight you are lifting.
That 1000 lbs (or whatever the listed limit is) is based on the length of the given beam. When you extend that beam further than it was intended, you reduce the limit of what the structure will safely support. I don't remember the exact formula off the top of my head, but simple mechanics will tell you that this is so.
04 Mustang GT vert basically stock
88 Dodge Ramcharger 4X4 for those things a Mustang just can't (or shouldn't?) do.
98 Ford Taurus SE Comfort --- wify's ride.