Beginner Road Track Racing: Feedback on Engine Options Wanted

With lots of twisties and only one straight, go for the torque of the 5.9.
One suggestion:
If your track offers a driver's school, take it. You'll get some track time with a seasoned instructor and a prepared car. You'll get to learn the particulars of the track, and see for yourself what you'll want the car to do and how it should act; and be able to plan your build accordingly. And you'll be able to network with other drivers/racers/instructors and possibly gain some input that way.
Thanks. Wanting the torque of the 5.9 makes sense to me with all the turns.

Great advice on the training, which I intend on doing. I spoke to the track last year, and they indeed have a handful of drivers who train either in a loaner car or in my car. I didn't consider doing the training now in a loaner since it will be a newer car unlike the Valiant, but that might not be a bad idea since I won't start building the car until next year at the earliest and probably won't be on the track until 2026. Being in the car with a highly skilled driver and being able to discuss my build can't hurt.

A good friend of mine who has pushed me in the road racing direction runs time laps in his 2020 Audi at this track, and I've ridden passenger on a couple track days with him. He knows nothing about driving a classic car, though. While I can get some good pointers from him on general driving and the track, he's out of his realm if he leaves the comfort of an all wheel drive, traction controlled car with huge wheels and brakes. I doubt he'd even drive the Valiant if I offered. He suggested I also look into joining a local club since they might have classic car drivers who train.