You don`t reuse old springs, you only use the springs that came with the cam. The cam you have is on the small side and won`t require a weaker spring to do break in procedure. Cam break in with weaker springs is only needed when your sure enough trying to break in a cam that`s huge and has mammoth sized springs on it. What happens is, the spring pressure on heavy duty springs is so high, it forces the oil wedge off the cam which ruins it.
Since the block is zero decked, your going to have to check valve train geometry after it`s assembled to know what lenth push rods to get.
If it were I, I would use a .041 thickness gasket with a zero deck.
After you get your valve train set up, make sure you break it in with lube that has ZDDP in it or the cam will go flat. The Valvoline race oil has it and works well for cam break in. You`ll have to keep using it there after to make sure the cam survives.