| Angus,
If you buy new head gaskets you can get 916/ST4 gaskets which are plain steel and thinner than the original black fibre 888 head gaskets. The originals are 1.3mm but I don't have the thickness of the steel head gaskets. I would guess they are 0.7mm which would give the same head to piston clearance using 0.9mm base gaskets instead of 0.3mm.
Standard clearance from head to piston is around 1.4mm but you can reduce this to 1.0 mm safely. Using 0.3mm base gaskets with 0.7mm head gaskets would reduce the clearance to only 0.8mm which is too close, but check the plain steel head gasket thickness. 1.3mm head gaskets and no base gasket works out fine.
To be sure check the squish with solder between the head and piston. | 
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