A bit late as usual, but here goes.

The engine in the KB10 differs from the A10 engines in other models in the following areas & this is gleaned from my parts book.

Cylinder head. Half a point more compression. Pistons are the same but the head has a different part number for the KB10.

Exhaust manifold. Dual outlet design but with provision for stock, single carb inlet manifold heating. Just the ticket for a 'stock' 1200 engine & as a bonus it has no flapper valve shaft to leak & make noise.

Distributor. Different cam for the points & different advance curve.

Carb. Different sub model with different jetting.

This added up to an additional 4hp at something like 6,000 rpm. It should be noted that the coupe is the heaviest in the B10 range so this was possibly done to allow it to keep up with the others LOL.