CA18DXX already has 34.15mm inlet valves from factory
these are quite large valves well capable of 400+hp.
Just need longer duration inlet and exhaust camshaft.
This is done simply using factory exhaust cam on the inlet
side and getting a custom grind for the exhaust.
Simple & less money spent for Lil gains on already big inlets.

The factory Ex. cams have longer duration so put them on the
inlet side then get a custom exhaust camshaft for the exhaust
side for more duration and ready to go focus on other areas
of the package to support the hp required.

The inferior size but famous Honda D16 1.6 sohc 16v turbo
engine makes over 450+hp with stock 26mm exhaust valves
and 30mm inlets the most is 31mm inlets for these 76mm bore
engines and using cast suzuki vitara pistons with 24+ psi.

A CA18Dxx head is already a great as not many hydraulic
lifter heads of this size can spin to 8500rpm before needing
to go solid lifters for more rpm.