I recommend that you purchase the styrofoam foatation from Flying Scot, Inc.  I recently purchased the flotation from them and am in the process of installing it.  My original styrofoam was 'pilling' or 'shedding' and was in the process of solwoly filling my 1970 vintage boat with little styrofoam balls. 
The installation is not particularrly hard, but it is very helpful to be able to turn the boat over and set it up on saw horses or some other supports that are high enough to enable you to work standing up underneath the boat.  I cut the old fiberglass straps that hold the flotation with a dremel tool.  Then sanded the areas on the seat bottoms and hull sides where the old straps where attached.  I was then able to remove the old styrofoam - at least, what was left of it - and install the new flotation blocks.  I then cut six 24" strips of 2" wide fiberglass 'tape' and glassed / epoxied the middle 11"  of each strip.  Once that had dried over night, I was able to glass / epoxy in the strips to the hull sides and seat bottoms in place of each of the 'old' straps. 
The new flotation kit also comes with two longditudinal web straps and wooden blocks and stainless holding straps.  The blocks are also glassed to the hull - really the underside of the deck - in front of and just behind the new styrofoam blocks.  Once the epoxy has dried, the web straps are atached to the blocks with the stainless straps.  These hold the new stryfoam blocks in place fore and aft.
The whole process took about three days total due to the expoxy drying time.  The only hard part is getting enough friends together to get the boat off the trailer, turned over and lifted onto and later off of the saw horses so that the work can be done reasonably easily.
Bill Harshman, FS 1891