ok, since the patch worked to fix the missing lines in constructor.gd it means you had the wrong constructor.gd file. I always worry when I'm updating files/links that someone is going to download in the middle and get a main file and patch that don't match or similar, so I suppose it is remotely possible that happened to you. The easiest fix if that's the case would be to redownload the main files and do that clean install once again. I assume you're not resetting/applying mods in game or anything else not in the instructions from what you've said, but somehow or another you had mismatched scripts (constructor.gd was out of date, but races.gd was current).
That said the errors you're getting now could be a legit bug. It hasn't affected my gameplay and I couldn't replicate it, but I can see a spot in my added code that could possibly end up trying to pass a float as a string and screw things up. So, I'm updating the files. Wait until you see "EDIT9: ..." on the original post and then try downloading again. You can apply the patch again (it's updated now) and see if these last errors go away for fun, but I'd still recommend a clean install since there were mismatched files just in case there are other outdated scripts in your current install.