Right go onto CGB & look at the prices.
New pistons & liners, liner seals, bottom end set, headgasket set, coolant & oils(get cheapo oil x 2 & 1 lot of decent stuff) 3x oil filters (yep 3) main shells, big end shells (don't mix the end caps up off the pistons they are matched

) sump sealant.
Prob get all you need for a full rebuild for around £500 or so, maybe less.
If you don't have a cam fitted & have the cash get one, with the springs & vernier prob looking at £250
Once rebuilt, run up to temp, dump oil, change filter, new cheapo oil in, run at 1 bar boost or less & drive gently but still boost her now & again, this helps bed the rings in. If you have fitted a cam you have to run it in @ 2k rpms i think anyway. 250 miles dump oil, change filter & put in decent oil & drive however you like.