Unless you buy a "balanced kit" from one source you will ALWAYS have to have the assembly balanced. In the aftermarket world, while 8 pistons may well come in within a gram or two of each other, rods the same way, there is NO standardization of weights between manufacturers. And many manufacturers have different lines of the same parts that have different weights.

So you can see that buying parts from two or three different manufacturers or suppliers, you will need to have the assembly balanced. A previous poster told you where you can do this in the UK.

R.