PDB said:

So if I follow you, basically you the take the luma/luminnce from the BR which contains all the detail information and overlay the color information from the laserdisc. ... I remember there was a AVIsynth script that did something like that. ... When I first tried color correction, I used colourlike/colourlikeFBF and could never get the results to what I wanted.

I never could get that script to work on the system I was using (with all it's Avisynth plugins, something must've conflicted). But, yes, the approach works only within narrow parameters. (They were having trouble with crushed & blown-out areas that simply wouldn't translate right.)

Here's my test. You've got the procedure right.

The Laserdisc provides the coloring (Hue, Saturation):

As shown, the pan & scan Laserdisc had to be resized and aligned to match the Blu-ray (always a pain to do in a paint program).

Just a note here: The source of the Laserdisc had pretty bad color-clumping that showed up ugly when the brightness (inherited from the Blu-ray) was lowered. I had to blur-smooth it to make the color more uniform in the final mix.

The Blu-ray provides the detail (Luminance):

And the combined H-S & L result is ..

Hmm. This looks a little underwhelming.

Aside from the fact that the Laserdisc rip's noise is coming through, the Blu-ray has some of it's own. They don't mix well and inheriting of the Blu-ray's darkness, to get it's detail, darkens and changes the coloring.

Your earlier posted regrade looks cleaner and more naturally like the Laserdisc:

And I'm guessing a (working) Avisynth script probably won't do better than the paint program demonstration.
It looks like regular color correction is the right approach. I would suggest, if you're going for a match to the Laserdisc, reducing Speedgrade's contrast a little. The face brightness range is a good measure, but it's hard to tell using these LCD monitors with their critical viewing angles.