71 Demon 340 Gas Cap??

I am converting my '71 Scamp to the older style gas tank since my tank rusted and I just happened to have a new older style tank.
I didn't realize the cap threaded on differently until I read this thread.
So, I may have to change to an older filler neck also to use a vented cap. I'll check it out and get back to you. If I have to change everything I'll have my original cap I can get rid of.
Dallas