The battery on my electronic calipers is flat so I can't measure the drill size that would be suitable. But it should be really small, very much smaller than the holes on the 144th kit.
I think I will be safe with using a 0.5mm (.019") drill bit, as the U-Brass instructions call for a 1.0mm drill bit in 72nd scale.
Going by your photos the 12 holes on the Revell kit they look too far forward to me. When you drill new ones it would be best to position them a bit farther back. Perhaps you could align the first hole with the front of the torpedo door?
Looking at the stock hole positions, I think that starting the 1st new hole at the 2nd stock hole will be good; that hole is in line with the forward edge of the torpedo door. The vertical rivet rows should then fall nicely between the new holes.
U 215 was a Krupp boat and had 12 equally spaced holes on both sides.
Great! I have created my templates, which I will print on clear labels (Avery 7662). I can then apply them to the hull, aligning everything properly, and then drill the holes.
Thank you very much, Dougie.