Source parts are a mixed bag IMO. Great value - but need some attention to be "right". The cranks are usually usable depending on the machinist. That's beacuse they all have taper on them in some amount that can be measured. If it's within factory tolerance and not a race engine I don't worry myself - but there are others that do, and there are those instances where the taper is out of specs. If it's a race engine you're better served to get a crank from a better quality source. The rods have never used the right oil on the threads from the get-go so if you get them & use the ARP lube and torque values, then cycle them they will be out of round on the big end. I always budget in a couple extra hundred to fix the rods and have the shop hone the pin bores. Sand paper as Source recommends is not the right way to do this... You'll also want to make sure you have the right rod bearings - they need a large chamfer on them. I do this by hand, some places sell them done. Either way works as long as it gets done and there's proper clearances. The pistons and rings are fine. I wouldn't order it balanced - have your shop handle that.
As far as block mods - you might need to clearance the internal oil pickup boss. I've had to on two, didn't on a third... Otherwise it all fits. If this is a street car then yes, use the dished pistons, pbuild it for a quench of .035, and have the heads milled as part of the check and correct to set the static compression where you want it. Run a cam of around 245° @ .050, and lift close to .600. I like solid flat tappets myself and yes, you'll need matching springs for the RPM heads so expect to change those too.
