Here's a idea. Use two 5 pounders. One mounted in the nose, plumbed to discharge into the cockpit. Then the other mounted in front of the passenger seat below the knees that would discharge into the engine room.
The thinking is a follows. The most likely fire is a carb, fuel line, fuel pump or some combination of those fire in the engine room. No need to gas yourself. Just put the engine room fire out.
Then the there's the big one. Pull them both and MOVE BABY MOVE!!!!!!! I would add remote fire pulls at the drivers side cowl near the gas fill.
I am more inclined to use one 5 pounder for both. one nozzle in the cockpit and one in the engine room. Then add a carry along Halon 2.5 pounder for the little carb fire that won't go out on it's own. Keep it handy in the cockpit.
But no matter what you decide you need fire suppression. Good thinking just asking the question. Promote fire systems in these cars at every opportunity.