One problem with the round chassis tubes is that extreme care must be taken when incrementally jacking up the front and rear in stages. On one occasion, when I was being a little over optimistic, it spat out the axle stand one one side! luckily it was the early stages and the wheels were still on and the axle stand fell over and didn't impale itself through anything. I am now super cautious during lifting the car, something which can usually be avoided as I have an inspection pit.
My advice is never remove the wheels unless you are certain everything is fine and dandy.
I have one of the roller type alloy jacks and had to replace the seals in it after 6 months! it would suddenly start to lower with no warning. I do the air purge whereby, with the valve open, one pumps the handle through it's full range 20 times, bloody nuisance, but it seems to help.
I also made a lipped plate that fits onto the lifting platform of the jack. On it I fabricated half piece of tube about 100mm long that matches the diameter of the chassis tubes. Then stuck a piece of thin rubber to save marking the chassis. I did this to give a secure positioning for the jack and it can't slip off. It also self-aligns and enables safe jack positioning as it's difficult to sight under a low car to exactly where it's lined up.
If your chassis is covered in filth/oil/crud a piece of rubber twixt chassis and axle stand can induce slippage once any angle other than a perfect 90 degs is surpassed.
Who'd of thought there was so much to getting a car up in the air!