Staples ;)
pinrestore.com sells the original style staples and gun if you want to
go original.
I used the standard staple gun from home depot for mine though.
Game plays great with the new playfield - while you're rebuilding it
consider putting a flipped-upside gate in the ball lock at the top, if
you get it correct in there it will prevent the ball fly through that
black knights have. Wish I'd taken a pic of it when I did it but
hopefully you can figure something out from that description.
I also put a plastic rod/ring from a stern game in the pop bumper, it's
quieter but more importantly, pops a lot faster for better reactions.