Which valve springs

I see “.640 lift Engle roller cam”

The springs have worked satisfactorily so far, and they tested good.
Just leave them in until you feel like they’re due for replacement.
If that’s now, then you need some more physical data.
-installed height
-open force at .640 lift
-diameters(ID/OD)

Then you can sift thru some catalogs to find a suitable replacement.

The Red Flag I see in the engine build list is the stock rods.
I’d keep the upper RPM limit fairly conservative with those in the motor.