A few more thoughts:

When you go to straighten out the new line set the end on the floor and have someone stand onit while you unroll the line along the floor. This is the easiest and best way to get it straight.

To take off the old line don't try to undo the end nuts. Cut the line with a pair of side cutter pliers next to the fitting and remove the fitting with a socket wrench. This is especially important if you are forced to reuse the fittings.

When you flare the line remember "european" flares are different. You only bulge the metal, skip the last step of upsetting the the metal into the flare.

Get new fittings, if they don't have the correct ones you can reuse the old ones as above although you might have to drill out the piece of tube. If they have european lines but not loose fittings you might buy a short line just for the fittings.

Hope this helps. Let us know how you make out.