Flotation: under-deck bouyancy for a mid 1960s hullmid

what can be used to replace the flotation blocks for under the seats? are plans available and/or procedure for doing so? thanks

I would first call Flying Scot directly and see what they recommend before doing anything, as this can be a big project and you will want to be sure of your plan before getting started.  I used the DOW bouyancy billets.  Hardware stores sell them for use under docks.  They can be sawed to fit rather nicely.  However, finding them is easy, but its mounting them under the seats is whats tricky.  Check the racing requirements first as I believe they need at least 1 1/2 inch wide nylon straps of three per each of the four sections, plus one longitudal strap on both port and starboard (bow to stern).  If the Flying Scot online company doesn't have a kit, then I would create some mounts on the hull underneath the seats to secure the strapping.  For the mounts, I would use some wood blocks glued on with fiberglass, and then screw the straps into those.

Flyingscot does carry replacement foam ,from what I remeber the shipping was high on this.  If you are thinking about racing , you need to check to see if there are any requirments on this. My boat is a 64 and I only use as a daysailer and have no plans of selling so I used Polyethalene foam same stuff as the pool noodles It is slightly less boyant ,but there is a lot of space under the seat mine is 3 inches thick  and I traced the old one and cut with an electric knife , I have 8 logs under my seats the same as flying scot ,but thicker, I now have more floatation then origanal ,. and on mine they used fiberglass straps 2 per log  to install and so did I . If you use fiberglass on regular foam you must put something inbetween or it will melt it . The poly will not melt.  Installing fiberglass upside down will be messy.