I am very cynical about engine builders in general. Not to say there aren’t a few that are honest hard working folk.
@NikG is absolutely right, and I will add that, there is nothing that engine tuners do that you cannot with a little patience, a few tools and time.
I will also say that I know nothing about SRP, and my comments are more general about the industry as a whole rather then slandering any particular company.
If there is something “Special” about that engine or the tuning done to it, why are they selling it? No major engine shop in their right mind will sell one of their “top” engines, they are reserved for their team drivers and special friends.
At best that engine is a new one that wasn’t up to whatever standard the shop has or at worst, it is one that has been used and abused and refurbished.
If you already have a 10C and it sound like you do, I would be learning as much as possible about the tuning of that engine, maximising everything about it and your driving, then once you are close to the front, go and find that magic engine, but it won’t be a regular priced engine that’s on a website. All the best engines are sold without ever being advertised.