My $.02 worth
You need two sets of blocks: One for the sheet and one for the afterguy. The sheet blocks should be as far aft as is practical: corner of the transom is optimal. You will need a second set of blocks (snatch block are best but very expensive) located at the widest part of your boat, just aft of the spreaders. The reason you need this second set is that when you are on a reach and your spin pole is set near the forestay, you will want to keep the afterguy off of the shrouds. If you are still using your sheet blocks (located far aft) for the guy, the line will have to bend around the shrouds and anything else on a straight line between the corner of your transom and the forestay. This would be bad.Two notes on topping lift and foreguy...The topping lift top block should be located midway (approx.) between the spreaders and the mast top. Not at the spreaders as is shown in the owner's manual (at least in mine). This gives you a much more vertical pull on the pole and will make releases easier. Also consider adding a clam or cam cleat on the mast so that the bowman can lift the pole during a set if he needs to.Consider a double-ended foreguy. That way the guy trimming the afterguy can also trim the foreguy.