Unless you are going to stroke it, or it's an A+ crank and rods, I'd favour the small journal over the large journal, particularly if you are going to rev it..
Don't use the Hepolite 8.8:1 pistons (21251) for turboing they are as you say.
I would use Hypatecs, from Minisport SA- who seem to be selling them cheap these days.
They are about 10:1 C/R, but have a pretty thick crown, so the dish can be made quite a bit bigger volume by turning in a lathe.
Also, 1275 heads can be opened out to 30cc by somebody who knows what they are doing.
Alternatively, if you have lotsa$$ you can get good turbo pistons from Avonbar etc in UK.
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
