Hi again Tim,
I think we have some basics that need to be covered here...
Wood is Always noted as "Wood size" example 2 X 4 or 4 X 4, which is the width and depth of the wood piece and then length, example 2 feet or 1 1/2 feet and so on... 2" X 4" X 8' equals 2 X 4 wood 8 feet in length (at least here in the US) LOL
So based on that you have what sizes pieces of wood and you want to make them be what size?
If you are possibly talking about attaching one 2X4 to another End to End to increase the over all length then you are asking for trouble in my opinion. If on the other hand you are talking about bolting two 2X4s together to make the equivalent of a 4X4 then that would be very doable...
-Bob