Hi
A long time ago I built a seven cylinder radial, I bought one of the large 2v lead acid cyclone battery and used a lead to each plug. Dont wire up each plug individually with your 6v battery or you will burn out the plugs
I would link the glow plugs like this :-
Run the positive lead to plug one, link two and three and four and five, attach the negative to the frame, this way all the plugs will get 1.2v not 6v
Hope this helps
Dougie