Actually the 300 has alot of virtues over a 351....and fast,I really doubt a 4.3L, 292, or a 225 would pull like a 300 will.
First off, the 300 has 7 main bearing, the 351 has 4. The bottom end is absoultly indestructable.
300's are very, almost scary simple to work on.
They are capable of tons of low end torque, they pull just as well as a 351, untill you get into 55-70 runs, then the extra 2 cylinders and 51CI come in handy.
300,000+ is not uncommon for a 300.
They have timing gears, not a chain, therefore they rarely (if ever) have timing issues.
Im not badmouthing the 351...i think its a great engine, and tons better then a 302, but the 300 is a good, hardworking engine that will do anything you ever want it to do.
later,
Dustin