You can do what you proposed by using an earlier block thus having the stonger rods, but the problem that will arise is the early blocks do not have the casting provision for oil feed for the VVTi actuation. This can be solved with some slight modifications to the block and heads and the use of stainless braided lines. That is probably a lot more work then whats its worth. You would be better just getting a set of the early rods and taring apart your lower end to swap out the rods.
I'll bet that if you posted a wanted to buy add on here, you should be able to get a set without much problem being that there are many members that have gone to aftermarket rods while insearch of high power levels.
Another option that I haven't heard of anyone trying yet with the rods that has proven to be of benifit in strength on other engines is the take your rods and have them cryo'd and shot peened. This has proven to strengthen them, Although this would still probably equate to a higher cost then getting a set of the early rods.
Another thing to remember, is its not the power and compression loads that destroys a rod, its the inertial and tensile loads that do the damage. The rod experiances the most damaging loads during the intake stroke. The intake stroke is the the worst stroke on a rod. The intake stroke is the only stroke that the rod is under tensile loads. Every other stroke, it is under compression loads and pretty much every solid object known to man is stonger in compression loads then they are in tensile loads. Look at the strength properties chart of any metal and you will see what Im talking about.
I always have built engines with the intent of achieving the desired power level well below the factory RPM limit by running more boost and other means rather then running higher RPM's as many do and I have never had problems with rods that were said to be weak or too weak for that power level. But in the case of a UZ, being that there are stonger rods out there that can be had for really cheap, its probably better off the be safe then possibly sorry.
