If I didn't already feel the stock steering was spot on, I would convert to electric pump mounted in the frunk that has variable assist so you can dial it in to your preference. That should also save some power and weight. The conversion is common enough to have control boxes that allow speed variable assistance etc. Having driven a couple of manual steering Ferraris (348 and a Mondial 3.2) I did not feel they were any improvement when driving and were worse at low speeds. Part of it was that the steering was slower, part was that I generally do not like higher steering effort. If I wanted to get more feel out of the stock steering I'd look to maximize the caster before touching anything else.
As others have said, an F50 steering wheel (and playing around with wheels and tires a bit) has mostly sorted out the steering feel issue on my car. It's to the point where I hardly ever think about it anymore. It's only when I get right out of one of my other cars with a really quick steering ratio and/or manual steering that I still notice the slow 355 rack to an extent, but it's much better than stock. Since you're local, you are welcome to try this set-up and see if it feels like enough of an improvement to you?
I would love to experiment with a steering ratio gear reducer, something that put the 355 rack around where other sports cars are. It's really got a shockingly tall ratio. I'm curious what the factory was thinking. https://www.summitracing.com/parts/hre-5225?seid=srese1&gclid=CjwKCAiAlPu9BhAjEiwA5NDSA_2ma6CmnkkgnpyZZN9VHfomi16ibHrA1nkNpUAxnZQA0a0G60OivRoCTWMQAvD_BwE
I have a manual 2.75 full lock-to-lock Challenge steering rack on my 355. Achieved the one must-improvement I wanted on 355Ch’s driving experience. I’ve driven the 355 back to back with known top-notch driving experiences such as 997GT3RS and 964 RSR build race car with Cup steering. 355 Ch hands down.
Period reviews praised the steering. It's just in the past few years that we've decided cars need to be so twitchy.
I don't know if reducing pump pressure would achieve what you want. Might just make the steering jumpy. As I understand it the best way is a larger diameter torsion bar inside the rack. Turn one ( turnonesteering.com ) said they can rebuild our rack and make a larger torsion bar for decreased assist for $1700 and 4-6 week turnaround. (these numbers are from last year) Also they said they could change the ratio but cost would be 5-10k and one year. (so no for me on that one)
