I always set the lash hot.

I checked my old UD lobe profile sheet....... Those .4176 lobes are listed as .026 lash with a 1.5 RR.
If you were trying to have the 0 lash point be the same going from the 1.5 to 1.6, then the lash would need to grow almost another .002.

If I had seen the TQ was so soft at under 4500rpm, I definitely would have tried loosening the lash from the .016/.018 they were running.

The basic bracket motor I did a few years ago was making about 100ft/lbs more at 4000, with the same intake and a flat tappet cam with a little more duration than the roller he's using.