All of them have the same block but the Civic Si Ep3.
The only difference on the Ep3 block is that it has smaller water passages and no oil squirters at the bottom.
The non existent oil squirters is not a problem at all, when using forged pistons because these pistons are designed to take the heat.
Basically they help cool the pistons, but forged pistons can handle much higher thermal loads anyway.
So yes, I would consider a k20a3 (civic Si block ) to be sent off to get sleeved but because I am not speaking from experience, if I were to spent $$$$$ to built a sleeved k motor, I would probably go with the k20a2 type motor since it is cheaper than the type r.
Now in your question, I figured you know that various blocks have different internals, liek rods, pistons, crank etc...
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