Power loss. 318 Vs 340 manifolds

I need to decide what Im doing exhaust wise on the Dart because Im just about ready to start it.

I really dont want to run headers on it, It just looks to stock under the hood and Im more concerned with ease of maintenance then anything right now.

Ive been considering using a set of early 318 manifolds seeing I cant really afford a $300 or $400 set of 34o manifolds right now. So my question is how much power will I loose on my mild motor.

Heres the details.

10:1 (actual) compression 360

Comp XE 268 224/230- 477/480 - 110lsa

302 casting heads
1.88, 1.60 valves
Stock sized 318 ports.

stock 71 340 cast iron intake (spread bore)
stock 72 340 800cfm Thermoquad.

The motor pulls to about 5500rpms

Thats it, Nothing fancy, pretty much stock parts.

So what do you think I will loose over the 340 manifolds ?