Looks like a nice fixer upper, do not give up on it, this one can be restored nicely!
As far as inside the helmet, I would guess that there would not be a metal plate to hold up the spike, normally do not see these on crucifrom bases.
I would think stars with bolts however I have seen both types.
There are numerous postings on this site about fixing up helmets that can help as well as excellant step by step guide to cleaning them up on Tony's site
http://kaisersbunker.com/preservation/index.htm
Just cleaning will do wonders!
good luck
James