Is there any information on how to bend the seat post properly without damaging anything?
I just take a bent axle, clamp the frame to the stand, have someone hold it and torque it
I have used leverage and force to open a seat opening. If I just need the space open I have used the scissor jack for my van with good results. If you need to open just one side use leverage. The longer the leaver the better. Is there a limit, yes, and if you have to move it back for a smaller seat at some point this does weaken things a little.
I tried this using a jack handle, it seemed like it was not going to bend, it was just digging into the frame.
I have few pictures on my build thread now. Generic advice is: assuming you are talking about an adult size kart, up to medium size seat, you can bend left post only using an old axle. Wedge it inside the triangle and bend it up or down depending on which way you want to bend the post. One hand on the kart axle, the other hand pushes or pulls the axle you are using as a lever. For seats Large and up, you will need to bend the right side post as well (not too much as seat may not clear the engine). Use a rubber-covered deadblow hammer and hit the upper side of the post while you keep the chassis down with your weight on the axle
I wholeheartedly disagree with this. Leave the right side strut alone. Deal with the offset.