Albert, in Sweden, SFRO (our IVA) wants you to prove that your welder is able to "brake" the steering column thickness (about 15mm) at max power with the arc, I guess to make sure you can get enough penetration into the column steel. They say if you can't achieve that, don't weld the steering column extension with this welder. Then they want you to drill 4 crossed holes at each end of the extension, and weld inside the holes as well as around the edge (this is not a big deal). So you can see that the steering column extension issue is very sensitive for SFRO, and I don't want to take any risk.
Now, we all have different skills, and most of you know that I'm new at welding, but I think I really improved along the way (I started my build a bit more than a year ago) and my welds on the chassis are descent now... but for 2 and 3mm wall thickness. What about welding a thick-wall tube on a plain 15mm shaft with my 145A, I don't know? That is the reason why I wanted to avoid, if I could, this welding part.
But is looks like I have no choice, and will make some tries and tests next week. The other problem is that I have very hard time to source this thick-wall 15mm inside diameter tube: I have to buy 6m anywhere I go, and it is a quite expensive (and a waste of more than 5m!). As I have ordered my wishbone to Talonmotorsports, I have no leftover of 19mm upper wishbone round tube.
So I will keep on thinking about that. I keep you posted.
Thanks to all of you for the replies and advises
Regards.