Intakes are pretty safe, seldom burn, I've found that a missed shift, with or without a weak spring, the ex valve can be "spanked" by the piston, and/or bend the pushrod, and poke it thru the rocker, leaving a witness mark on the piston.
Often, no valve damage occurs, just lose a cyl, and get a mean backfire, same as losing a lobe.
I used to carry spares in my glove box, right beside a spare ballast.
Cheers .