I'm assuming you have a 67-72 truck. You can set the 350 on the orginal 250 mounts. However the engine sits back 3 inches more than an original smallblock truck . The distributer is a tight fit but will clear the firewall,well at least the points distributer will.Also the fan will need a shroud to make sure it pulls enough air. The advantage of this is you don't need a different driveshaft. If you have a stick, the clutch linkage will need some work and may be a real pain with headers.