In and during the 50s & 60s everything usually fit just fine.
The Clifford manifold, which came along sometime later fits "tight" when running the Fentons.
A lot of "off shore" counterfiet parts have found their way into the marketplace too, as Brian points out. The 'tube headers' for the early engines are a Tiawang off spring and a copy of the Clark headers sold in the 50s. An 'extra' weld like Larry mentions is good "insurance" there also.
Happy trails.
