Measure the stickup of all 5 pistons to determine HG thickness. You never know if it was previously replaced with a wrong one, and if yo have a bent rod, it will show as a low piston.
If you are in europe, you can probably get a Viton coated MLS gasket which holds better, but requires a smoother surface to work properly. Goetz, Reinz, and Ajusa all sell them.
Your head will have to be drilled for 12MM bolts and washers, unless maybe you are feeling frisky with heliCoils.