No, jack stands under the corners of the frame would be the way to go if you're checking the frame. Like Dan said, you may need to check the floor for level. Or you could shim the jack stands so that the corners of the frame are level using a laser level, and then use that laser level as your vertical reference point. Something like THIS


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.