That's an interesting tuning you're using. I think I remember reading that Bobby Ingano uses a Bb on his 8th string, as you do, but I don't recall ever seeing a C6 tuning with D on the first string. What prompted you to do so? Something to do with the Blues? If so, I might need to rethink my own planned tuning for the 8-string---C-E-G-A-Bb-C-E-G. I know that putting the Bb where I plan to will mess things up in terms of using tabs others have written, but I find myself using tabs less and less, and it seems I always end up rewriting tabs others have written anyway, for a better fit with the music in my head. I like lush 7th chords, which are pretty difficult to come by without a string tuned specifically for that purpose, and I decided against putting the Bb on the bottom because it limits my options in terms of inversions. I also play with four picks so I have the option of richer chords..
Ok, will try to keep this brief. On my 8-string I wanted to keep a proper C6 in place on strings 2-7, so I could play/learn pure C6 without issues. I made string 8 a Bb, so that would give me a Dom7 chord with a straight bar. String 1 went to D as a re-entrant string per what George Piburn advocates in the DVDs shown below. Haven't had the chance to do anything with it yet, but I knew what I wanted.
https://www.georgeboards.com/songs.html Scroll down the page and click on "Basics and Blues", "Power Rock Method" and "D String On Top". DSOT is the DVD that corresponds to the tuning I will use. The other DVDs are pretty much the extent of the Blues DVDs available other than the links I posted earlier.
While one can play blues in C6 tuning (actually C6/Am7), the tuning functions much better for CW and Hawaiian music. The 6th of the tuning is a killer for blues playing and so the player must avoid it. It can be done with precision picking but it takes a lot of work.
Ryan makes some really nice guitars. I have seen pics of many of his lap steels.
There is no better forum than BGU for getting info on everything related to regular guitars and blues. I have been a member here for years.
However, since you play lap steel, though we have a few lap steelers on this forum, I strongly recommend you get on
https://www.steelguitarforum.com/. Great place to visit for info about pedal steels, lap steels, console steels as it pertains to technique, electronics and gear. A huge repository of knowledge over there too.
Between the 2 forums, if I have a question about gear/electronics, if I can't get an answer, there just isn't one to be had! Well worth the $5 sign-up fee.