998 and 1098 blocks
ARE the same height, bore, room inside etc. Basically same casting.. different engine #..
You can fit :
998 pistons and crank, or
1098 pistons & crank, or
Hillman Imp pistons & 1098 crank (if offset bored to 68.0mm) gives 1220cc. Not all blocks bore to this successfully, and you then need to rip about .140" off the deck so the pistons are somewhere near it.
I have also (years, nay- eons ago) put 1098 crank-rods-pistons into 850 blocks. But this needs the 850 block and main caps machining to make room. Not worth the trouble now- plenty of 998/1098 blocks about.
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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.