Essex v6

[caprispecial]

If its a choice between a standard oval port and a standard d port then the d port is much better.
But if the engine is to receive extensive modification then both engines would be fine except that the d port engine has thicker cylinder walls which will accept +060 and more and still have strong non porous walls.
Also be careful of the z car engine, lots of them were only two and a half litres.