Is it crazy to take a street Mustang up a mountain climb course?

I run a 67 Camaro in amateur hill climbs that's maybe one step more sorted than your Mustang, so I can tell you it's absolutely doable without turning it into a race car. The guys in full builds are going for times. You're going for seat time and a fun weekend, and there's a whole class of us doing exactly that in street cars with interior and carpet still in them. Brakes are where you shoud spend your money first, not suspension. A slow climb is actually easier on brakes than a highway pull since you're rarely on them, but the section transitions matter. Your gravel-to-pavement course means you'll want pads that handle heat without fading, and fresh fluid bled right before the event. Standard upgrade route: better pads, stainless lines, fresh rotors if yours are worn. You do not need big brakes for amateur class. What kills people's days is boiled fluid, not lack of stopping power.

The gravel and pavement split sounds scarier than it is. You just drive the two sections differently. Gravel rewards smooth and patient, pavement rewards commitment. Most first-timers are way too cautious on the pavement and way too eager on the gravel. Do a couple track days or autocrosses first if you can, and walk or drive the course slowly during practice if the club allows it. Knowing what's over each crest is worth more than any part you can buy.

Cooling is the one place I'd go beyond a bigger radiator. An old V8 crawling uphill in summer heat with no airflow is a genuinely rough situation, and these old engines were never great at shedding heat to begin with. Bigger radiator, yes, but also make sure your fan setup actually moves air at low speed, because that's your real problem on a 14 percent grade. A shrouded fan that pulls hard at idle matters more than radiator size. Check your timing too, since overly advanced timing makes these old motors run hot under load.

One practical thing: look up the tech inspection sheet for your local club now, not the week before. Most amateur classes for older cars need a roll bar at minimum, decent belts in good date, and a battery cutoff or fire extinguisher depending on the club. Budget a few hundred for that stuff and you're fine. It's a wallet-friendly hobby if you resist the slippery slope, which I have failed to do for six seasons now.

I build engines for a living and I've prepped maybe a dozen old carbureted V8s for hill work, and the thing nobody plans for is fuel. On a slow pull in July heat you can get vapor lock long before the gauge shows overheating. If yours still has the original mechanical pump and hard steel lines running close to the block, that's where the trouble starts. Wrapping or rerouting the fuel line away from exhaust heat is cheap insurance, and some guys just add a low-pressure electric pump as a backup. Also check what fuel you'll be buying at the nearest station to the event, beacuse a bad tank of low-octane in a high-compression old motor climbing under load will rattle itself silly.

This is making me feel better about my old F100 I was thinking of dragging up a similar course. My worry is the tires. Mine are just regular all-seasons with decent tread, and I keep picturing the gravel part being like driving on marbles. Do you guys run anything different on gravel, or just go slow and let the car do its thing? Also does the car feel way lighter or looser when the pavement part starts after all that loose stuff, or is the switch not that dramatic in person?

Ran my old Falcon up a similar mixed course a couple years back and the thing that got me wasn't the car, it was the schedule. Practice runs are early and you'll be wrenching at 6am if anything's off. Bring spares you can actually swap trackside, belts, a spare plug set, some hose clamps, and drag a buddy along. Second piece of advice, don't worry about your time at all on the first event. I got so focused on a number I drove worse, and once I stopped caring I was quicker anyway.

Update: the vapor lock comment hit home. I crawled under the car last weekend and my fuel line runs way too close to the exhaust on the passenger side, so I'm rerouting it this winter along with the pump. Also started a spares box after reading the Falcon advice, mostly hose clamps and belts so far. Still unsure on the tire thing for gravel but I'm leaning toward just taking it slow.