short term memory loss......
I did this a few years ago. To check the alignment, I leveled the plane laterally and used a long straight edge and had somebody hold it against the rudder trailing edge. I then just eyeballed "vertical". However, my original setup wore evenly. So, I "cheated" with the new spring. I used the old one and jigged it up on my drill press to match drill the new spring right through the old one. I then just checked it to make sure it looked good.
The tailspring/tailwheel comes with a dwg. that shows how they are drilled. 2 olts attach the tailwheel to the spring. One bolt attaches the spring inside the fuse.
I painted the tailspring and then had to strip the 6" or so that go into the fuse. It is a very tight fit. I was a little concerned about corrosion. But the 18 year old spring I took out was clean with just a coat of oil on it. I was pleasantly surprised.
Anyway, the setup doesn't appear to be TOO fussy. I think a good faith effort to get the plane laterally level and the tailwheel vertical should work fine for you.
Good luck.
John