No doubt the only real solution is headers.
If sticking with manifolds (I have) then you should cut through the webbing of the manifold between each port. You are still going to run quite a risk of your studs popping, but that's less of an expense than the manifolds cracking...... usually. I have read somewhere that using bolts rather than studs and nuts to secure the manifold eliminates problems, but I cannot vouch for that.
I believe that the "special manifolds" your mechanic is talking about would be headers. Google RV 454 headers
, or wait for a few tips here. I really don't think a person needs to buy the most expensive big name ones though.
Here's a Frinstance, since you say you have a 1997:
Summit Racing have everything from these up to a thousand bucks or so for big name ones.
Note: if you get headers, make sure you get full length
ones that will mate with your existing exhaust system without major modification. Avoid "shorty" headers.