Hmmmm in NSW it depends on a few things.
On a roundnose it doesn't seem to matter a rat's, fit whatever, BUT if you go over a 1098 block ie. fit a 1275 block they will want to see disc brakes.
My `64 850 previously had a 1982 1275A+ motor in it, with 45 Weber etc, no emissions gear in sight. Not a problem.
My `70 car has a `68 1100S block, same deal. Not a problem.
On late cars (Clubbies) though with compliance plates and subject to ADRs, you can get caught. We have a late `78 Clubbie 998, I rebuilt a 1098 out of a `74 Clubbie and stuck it in.
Trotted down to get a blue slip and the guy reckoned the motor was `too old'.. hello? the block is the same...

basically he was arguing about the engine number prefix.
(Didn't have air pump and the smog pipes on but he didn't care).
So I got the shits with him and left. Just drove it for a while regardless.
Not on the road at the moment- it's awaiting a facelift..
My advice on these cars is, if you want to make your late 998 into a 1098+, just stick a 1098 crank and oversize pistons in YOUR block. Saves a lot of aggro.

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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.
