O.K here is the concrete block and railway sleeper platform, this worked really well.
It helps to have someone else with you,
1. for safety should it go pear shaped
2. to keep an extra eye whilst going through the Jacking process.
As the boat was on the trailer I only had to jack it up around 200mm, just enough to add concrete blocks to the piles left and right and position the railway sleepers as needed.
And here she is below now suspended so that I can get all underneath and all around the Bilge keels to blast them, epoxy fill, primer and paint them. Once I have finished with the Bilge keels I will put her sitting on her bilge keels on the two block piles directly under the bilge keels in the photo below. Then it is a matter of reversing this process to get her on the trailer before painting the hull. Meanwhile the trailer will be out of the way giving good access.