I built 2 versions of this a few weeks ago just screwing around and it works great.  Its MUCH faster than goofing around with the press and can be a solid useful tool if you are in an apt with no access to a press.   IT may do head spacing depending on how tight your trunnion is and if you build a smidge different.  

I really need to try building something like that. If anything just for the fun of it.