Hi Geir Ove
I just bought a 169 sqm Parasailor for my L450.
I am not sure on the size of blocks, but if they are the same size as for your halyards, then you are on the safe side already. You will need four blocks.
I am explaining the set up, just to make sure you have the right information for the location of the blocks.
Two of the blocks need to be right at the bow, outside of your fwd life lines. You use the fwd blocks for the guys going to the heads of the Parasailor. This keeps the leading edge or luff relatively tight down to the bow if you are not going dead downwind).
The other blocks have to be really far aft on the boat, again right on the outside. Through these you lead the sheets
to the clews (trailing edge, or leech) of the sail. They need to be so far aft to be able to do close reaching (apparent wind
90 to 70 deg) with the Parasailor. For this will need pull the clew way back on the boat. For deeper downwind in strong winds if the clew flies too high, you can always put a barber-hauler or tweaker on the sheet. These are usually tied to the the mid-ship cleat or a strong point nearby.
So each lower corner of the sail gets two lines, a guy and a sheet. Only one per corner point is active at any time. The other line is lazy, doing nothing. When gybing, you just make the tight lines loose (lazy) and trim in the previously lazy lines in to set the sail properly.
So make sure you pick the right location for the the blocks.
BTW - just came back from a great sail to a little resort on South Pender Island for a late lunch. Had great wind
(up to 23 knots true and sunshine). With a full cockpit
enclosure we did not even need a jacket, and that in Canada