[piecesparts]

Take a look at the block (just below the passenger side head). Is the tab (where the number is stamped) a long one? The later motors had a short piece that the number was stamped into and the older (heavy block) had the longer tab. In most cases the tab is an indicator of the desirable blocks and supports the fact that the block may also have the 4 bolt mains.

I understand the thought of buying a motor that is rebuilt and ready, but I favor the thought of KNOWING what I have. I would look at the investment of doing the rebuild of the motor in the truck vice buying a motor with an UNKNOWN item to it. Who rebuilt it and how good of a mechanic are they? I have seen some guys do really crappy work and the motor run great for about a year or so. I believe you get what you pay for and I have in the past. The motor that is overcarbed will most undoubtedly have a large amount of deposits on the valves and this can influence performance.