when swapping a Holly from a 305 onto a 350, is any work needed other than just taking it off one and putting it on the other?

 

To do it properly, you'll probably have to change the main jets and power valve (unless it was over-jetted for the 305). You'll almost certainly have to adjust the idle mixture rate.

 

Holley claims the idle mixture srews once set are near perfect for any setup and the only change nessasary are jets and possibly power valves. Depending on how different this enigne is compared to the other it may not need too many adjustments. like Vader touched on it may have been jetted rich in the past. Factory Holley settings are on avarage 2% rich so it may be just right. I could slap my Holley on just about any engine and it would be fine without changing anything.