Here's a page with some answers to questions that are regularly posted into the message board
Here are the measurements of the lifting keel centre plate.
Please note that the measurements were taken from a badly corroded centre plate. If you use this as a template you may have to do a bit of fine tuning with an angle grinder
A-F length top to bottom 105cm
B-D radius 11cm
E-I length of the front 79cm
C-J length of back 85cm
G-H width of bottom (above the curved corners) 25cm
E-K width of top 36cm
Steel thickness 5mm. The rest is hard to measure but hopefully can be worked out by printing the photo out and working out the scale.