Whats the diff. in 305, 350, and 400 ci engine blocks? I always have the most trouble with the easy ones

 

the bore mainly. The 305 and 350 had the same stroke, but due to the 305's water jacket configuration, it can't be bored to a 350(that probably answers your next question). The 400 used a longer stroke and a slightly bigger bore then the 350. A 350 with a 400 crank makes a 383 and a 305 makes a 333 or something along those lines, furthering the SBC's problem with long stroke/small piston. A 400 with a 350 crank makes a motor that makes less torque but screams to an ungodly redline.