Hi Wali, I think a good electronic ignition and a fancy spark plug would give you the horses, with or without the second plug.
The only advantage I can see with a second plug is the possibility that one might break down.
I assume you are using alcohol fuel?. When racing, I had one of those old KLG plug tester / sandblaster machines you used to see in garages. I was amazed at the number of plugs that didn't produce a fat spark after very little use with methanol. IHMO, this would be a better use of the funds.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.