You don't say if your 350 engine has any upgrades such as camshaft, heads, intake, etc. But here is an article to help recurve your distributor and set your timing. http://www.crankshaftcoalition.com/w...EI_distributor
With most aftermarket camshafts they need more initial timing. This also means you have adjust the distributor for less mechanical timing. Your vacuum advance will probably need a kit too.