Imp 68mm pistons will go on a 1098 crank (with block decked .140") but with a 998 they will be another 0.148" further down the bore..
Toss a 1098 crank in, you will get 1220cc approx. But good Imp pistons are very bloody dear now, have to get in from UK or NZ..
<edit> to get a 998 or 1098 block (same thing) out to 68mm you will have to offset the bores. Otherwise you will bore into the main oil feed line from oil pump to relief valve..
Check Vizard's yellow book.
These days it's all too much trouble.
Easier to find a 1275 block and bore that sucker to 1360 or 1380. As I did..

Or stroke it too, for even more cc, as I will on the next one!
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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.
