The guys racing the Euro SC motor (3.0L, 9.8:1 CR, CIS injection, stock heads)are having trouble without running race gas or an equivalent. Breaking rings or lands or something similar. Mind you, they aren't at 5,000 feet and above all the time, but something to consider.

Me, if I was going for pump gas I'd activate the twin plug feature from the get go. I realize that these SCs have stock CIS cams, and you can run a wilder cam with a lower dynamic compression ratio, which gives you some lee way. But the early Electromotive twin plug crank fire setup ought to be fairly cheap nowadays, since high end hot rods and track cars tend to go for EFI along with crank fire in one unit. The expense may be mostly in what you are doing anyway - machining the heads for twin plugging. PM me if interested, as I have one spare for just that reason.