I've recently finished refurbishing a mk1 Mercury with some excellent feedback and advice provided by various members in the collectable section of the forum. I put on an alloy piston head and also added a guide and top hat (chambers I think) together with a piston sleeve made in 0.004" ( 263934584802) and a couple of shim washers at the front of the spring between the spring and sleeve ( 132407910887) although you'd obviously have to check sizes on both to see if they were right for you. Link to piccies below of preload that there is in my example with a new "standard" chambers spring.
Best tip I had for getting it all back together was from T20 which was to check at what point the threads on the back block and the compression tube engage without the spring in. Then when it comes to compressing the spring and trying to screw the two parts together at the same time you'll be able to roughly line them up and have a better chance of getting them engaged quickly. Makes it so much easier.
http://imgur.com/a/j8To8vb
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