Around my home it's surprisingly hard to find a HVAC guy who knows the real science. Sometimes local HVAC companies will have a ME on staff who can look at it properly. Commercial guys generally seem to know more about the science. I'd try one of those routes, just to see. Many of the smaller companies here are just good ol' boys witha Duc-o-later calculator and don't know what a Manual J or Manual D calculation is. No education in the science. To make it worse it's an often arrogant trade on top of it, and a lot of them hate DIY'ers. There's some justification in that becasue one needs to understand the science, particularly with refrigeration, but the irony for me has been the most arrogant ones knew the least and thought they knew the most. The "pros" who I hired to do my main house really hosed it. I designed the basement system correctly. And if I hadn't it would heve been screwed up, too.
Not to worry you, but you can hose it if you don't know what you are doing. Many of those who think they know what they are doing get it wrong anyway. I'd at least seek out an experienced opinion. There are a couple of HVAC guuys here on the forum who are "freindly" (sorry don't remember any names). You might start a specific thread on the specific issue and see if they would chime in. I'd offer more help, but I just know enough about it from (bad) experience to know it can be done wrong.