Exhaust on 64 Barracuda?

So finally getting the car to the muffler shop next week for exhaust work. It has a 318 in it and I believe factory manifolds. The guy asked me if I knew if the manifolds would accept 2.5 pipe cause that is what I was going to go with. Any buddy know if the will? I don't think I need 2.5 inch right now but the car is set for my dad but will want to do it with a built motor in a few years so I am trying to think ahead. Am I thinking this through correctly? Any suggestions appreciated.

I just had my 65 barracuda exhaust redone... I wanted 2.5" from the exhaust manifolds all the way back but once he got the car up on the lift he had to do 1.75" down tubes from the manifolds then from there he did 2.5" the rest of the way... He said he couldn't go any bigger or else he'd hit the steering linkage... AND it ended up costing me more, cause he had to 'special order' 1.75 mandrel bent piping... All said and done, I'm glad I did it... It runs so much better now. I'm still running a 273, and it runs fine with 2.5". Went with magnaflows, sounds great.