Nova, performance lacking, what to do?

Hi Everyone!  
So I pickup up this Nova a few months back, got somewhat of a deal but she needed a lot of work as she had a 305 and the previous owner put a 350 in from an 83 Blazer.  Very amateur work, so about $800 later the engine is stable now, I've got some new front shocks, dual flowmasters and water/oil gauge.  Gas mileage is okay, can't complain but the speed just isn't there, and seemed to have decreased after the flowmasters were put on.  They told me at Midas (pretty reputable shop nearby) that the manifold was a 305 manifold, but that they worked with it.  Could this be why the performance dropped a bit?  also, i found out the carb is going bad as the car randomly shuts off sometimes when idling and is hard to start back up but I'm living with this for now.  Here's the big question -
Today I sort of got into an acceleration war with this honda accord ex(maybe a 2004 or 2006) and he almost beat me.  I thought V8's were faster than that!  So what should I put into my engine?  350 manifold?  Holley 650 carb?  Headers?  All of the above?  It's a dialy driver and I like the mileage but want more "VRROOOM!" hehe..  Thanks for any advice.  

what are the casting numbers off the block and heads? Is the 350 stock ?  What year motor is it?  

You need intake manifold, carb, and cam upgrades for your 350 to get performance up.  

+1  

if it does have a 305 manifold on it, your going to be starving the engine for air which can cause the symptoms you describe, so I'd start there. arguably, a 350 flowmaster isn't going to have enough airflow through it which can actually cut your horsepower (a little) more.  I would also suggest a second opinion at your local speed shop, I'm a little leery Midas's as a whole, but if you trust them I won't argue. Good luck and let us know how it goes  

I should add, opening up in intake manifold will negate the problem with the flowmaster  

More information about your NOVA is needed so as to help with your performance problem.
1.  Year of NOVA
2.  AXLE RATIO
3.  TIRE SIZE
4.  IGNITION TYPE
5.  TRANNY TYPE
6.  CARB TYPE

NOTE
The 83 BLAZER 350 is a good solid engine built for low speed high torque applications such as towing and off road running. This was determined by cam selection and ignition tuning. As I remember IN 83 GM used computer controled carbs & ignition. Usually an electronic q jet.

Knowing what you have will really help.