Don't forget to replace the dip tube O rings too and use some keg lube on all of the seals.
No reason why not. Just be aware that, unless you have an oilless compressor, you'll need to do a good cleaning of all parts, including posts, poppets and dip tubes to get rid of any residual oil before use.
As for taking to a welding shop to check, for what that would cost, you'd likely be able to have several CO2 cylinders filled.