How much power are you planning on making? 2.5" is probably fine up to the point where you would need a built short block but if you're close to that point it may be worth stepping up to 3" while you're at it.
FWIW, the early S197 GT500s only had 2.5" and I'm pretty sure they only stepped it up to 2.75" on the later ones.
Mid 300’s so it sounds like I will be good! Thanks!