These are far superior to the older engines.
Why is because the Vortec 350 comes with a factory roller cam. They also have a windage tray for better oil control. The crankshafts are "indexed" at the factory, meaning it has it`s true stroke depth of 3.480. The crankshaft is a 1 piece seal design that uses a flywheel with weights on it for it`s balance. The old 2 piece leak prone design used a different flywheel, but the good news is, the old 2 piece and 1 piece flywheels do not interchange so you can`t get it wrong.
The Vortec 350 should also have PM rods which are stronger rods than the old "X" rods and etc. The Vortec uses Metric rings, so if you plan to do a rering job, the rings are expensive. You can get a aftermarket cam to replace the stocker and reuse the factory roller lifters, this is a advantage as you can run a roller cam without going broke. If the heads aren`t included that`s a shame, as the Vortec heads are far better than the old smogger and camel back heads. The last thing is, some Vortec blocks have a provision for a mechanical fuel pump, some did not. Some are half finished, some aren`t even started. Vortecs also use a special timing chain. If you want to use something other than the stock replacement chain, Cloyes makes a timing set for it that`s a single roller design. Are the pistons the factory pistons?