What I do with small blocks is find out what the oem bobweight is/was. Then find all the weights of the oem parts and then you can look at approx weights of the parts your wanting to use and fiddle faddle to get them to that bobweight.

You can make or loose weight easily with wrist pin changes and removing extra rod weight weather the beams or the heavy weight on the rod cap.

You can loose 3-4 grams off the big end of the rod by using like a king Al bearing vs a std clevite.

You can get some weight from the piston and if I need the lower rod weight and ive one rods that even like six grams off vs removing six grams from the seven rod caps I run a bead on the bottom of the cap and clean it up.

But really if its a low rpm budget build, ive found you can get a decent balance job for under 200 if you mix and match things so they just need to remove weight.

As for how much you can be off, meh, many have mixed thoughts but one thing you can do on your own to help is make each rod/piston combo dead on the same.

Maybe not so much the BB stuff but ive found it semi easy to find the all the oem weights for a certain motor/year on the web.