No need to retap the block flange for a road car, they are 1/4 UNF the same as a manual and in the same place. Just unscrew all the studs and toss them.
Racers used to (maybe still do) tap the block out to 5/16 UNF and drill the gearbox flange to suit. Folklore says this was because thin flange blocks used to leak at the gasket. Maybe true because Vizard said so,

but I've never seen it happen on a road car.
Most 1100S auto and all 1300 auto blocks are thick flange anyway.
Hints (if you didn't read my auto block mod thread):
1.The relief valve seat MUST be removed before drilling the relief valve to oil pump hole. Because the oil hole is offset sideways a mm or two, you can't get the 8.5mm long series drill in there straight with the seat in place. It is tapped 3/8 UNC, use a head stud, spacer, washer & nut to remove it.
2. There are 2 holes drilled in the relief valve seat, these MUST be blocked (I braze them up) or else fit a manual relief valve seat instead.
3. The oil pump spacer MUST be bolted into the block before you drill from the relief valve to the pump. Because, this hole will be 1/2 in the spacer and 1/2 in the block when drilled.
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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.
