Try this: I have fitted sleeves to many '77s.
MAKING A PISTON LINER

Piston liner; I do not have dimensions but here is a quick guide to how I make them: Empty beer can, tall type i.e. taller than the piston is long. Cut sides off to form a sheet. Make sure sides and ends are square to each other. Get sheet of paper and roll into a tube ... put in piston and mark where sides overlap and the correct depth of the piston. Measure and transfer measurements to the steel sheet. Cut sheet but add 5mm to the length. I now have a bit of plastic tubing that fits over the piston rod but goes inside the piston. Roll the sheet around this tube and insert into the piston, but not all the way: leave about an inch out as you need to remove the sheet in a minute: Mark the sheet if the sides overlap. Remove and trim to size so the sides do not overlap. Now mark a line 5mm in from one end and cut crenelations (beautiful word that, fancy word for tabs) along the end and down to the line ... I use ordinary scissors for the cuts. Cut out every other tab out so the end looks a bit like a castle battlement. Put sheet around plastic tube again and fold the tabs down 90 degrees. Place tube and sheet into piston with the join away from the piston linkage slot. Push to bottom of piston, remove plastic tube. I now add a steel/delrin washer inside the piston to sit over the tabs. Add this and push into place with the mainspring. Job done.

You could of course ignore using the paper sheet and go straight to using the steel sheet for the first measurement ... but you may still need to make a fine adjustment for the final product.
And you get to drink the beer.

Cheers, Phil