OP -- Excellent choice on going with the 302! I was going to footstomp what Ed said, but ...
I know everyone is entitled to their own opinion as to how to do anything to their own truck but the reality of the v-8 "upgrade" to the '47 - '55 1st series trucks is that it is a LOT of work, fabrication and frustration to achieve marginal performance improvements required by the average Stovebolter (defined as some who doesn't want to mess too much with the truck's originality and just wants to drive comfortably/safely in modern traffic. Not all Stovebolters need to haul 70K loads at 70 MPH and do the Quarter Mile in .7 seconds.
You'll be amazed at how much that 302 will do for you, especially if you go the simple/easy step of replacing the center section of the rear axle with a 4.11 gear set. You even get to keep that venerable SM-420! And it's pretty much a bolt in with no getting crazy with fabricating engine mounts, rerouting exhausts and steering boxes to make that silly SBC fit where it doesn't belong. :P
