12G940 or 12G1316 heads off a 1275 work OK on a smallbore, IF you notch the block to clear the exhaust valves. They might give less low down torque than a well worked 202 or 295 head but you don't have to shell out big $$$ to pay for the porting. One is going on my 1132 Moke.
A bit of a cleanup inside in the valve bowl areas is all the 1275 ones need for a smallbore.
You do NOT want or need dirty big ports, particularly on a 998.
Yes some people get away without notching the block, IF the valves are worn into the seats and IF the cam isn't high lift and IF using stock rockers. I don't recommend this though, bounce the valves once and you will bend em.

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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.
