I think the term "Kantian constructivism" as an oxymoron. Kant was a constructivist about mathematics, but not about ethics.

I think it is clear that what we ought to do has to be independent of our decisions about what to do, and independent of any procedures we might use in making such decisions.

When people think that moral problems can be solved by some simple strategy of calculation, that sets them up for ghastly overreaching. They think they can turn everything into a "science" the way mechanics was turned into a science in the seventeeth century. They want to turn everything over to technocrats and social engineers. They become shortsighted or simplistic about their ends, and they disastrously overestimate their ability to acquire the information they need to make the needed calculations.

In the mid-1960s, as hard to believe as it may be now, choosing to go into academic philosophy was not an imprudent career choice. There were lots of academic jobs in philosophy then.

Kant was a rational theologian. He did not pretend to be a biblical or revealed theologian.

Kant considers belief in God and immortality to be items of "faith" because he relates faith to the pursuit of ends - in this case, the highest good.

What is central to morality is rational self-constraint (acting from duty), in cease where there is no other incentive to do your duty except that the moral law commands it.