If you had a Dave Williams Halfset and were looking to add regs. would you make it a 3/4 or Fullset? My intuition is telling me 3/4 so you wouldn’t have to mess with drilling into the original set. Curious to hear other views.
Thanks,
You could always have a set of regulators made on a new stock and keep the Williams stock safe in case you wanted to return it to original. Some makers might prefer to do it that way anyhow.
Someone else had a similar dilemma. Seth Gallagher made regulators for someone who had a Froment 1/2 set:
I believe that the Froment half set already had a Bass regulator bar mounted by Froment prior to Seth’s regulators.
+1 That would be my solution as well.
The mainstock idea could be the way to go. Would drilling into the Original mainstock and adding a bass reg. hurt the value of the set? In terms of resale.
Is the set a keeper? 
If I had a classic Ferrari, and was thinking of it as an investment, I would try keep it completely stock - or make additions that aren’t permanantly altering the car, like adding flashy spinner rims - As that would be more desirable for resale.
If I was going to keep the Ferrari, and enjoy it for the rest of my life - I’d paint it hot pink, grow a mullet and drive around all day blaring Whitesnake - but that’s how I roll.
I think I would drop the cash for a new mainstock… a hot pink one from Seth Hamon. 
If it was my set it just add the regulators to it. But all depends on the quality of the regulators. I don’t like seeing good pipes as a investment, they should be played.
Who will make your regulators?
Patrick
Probably, but is resale value the best way to settle the question? Seems like the real question would be: Would someone other than the late lamented maker, drilling into the original mainstock, have a clear idea how to do it in a way that would not disturb the original design, screw up the airflow and therefore the balance between chanter and everything else, and eff up the sound and playability of the set permanently?
If they were my pipes, I’d want to know that the potential regulator maker had very thoroughly studied and analyzed the existing system (perhaps another Williams full set), knew how it was intended to work, and understood all the consequences of the changes he or she was planning to make.
If its a Williams set then probably Marcus Coulter would be the natural choice to do any alterations as I think he did some work with Dave. Marcus is a member of this forum so you could contact him and ask his opinion. Hope that helps
Seth Gallagher will be making the Regs. I had a lengthy conversation with him and he seemed confident with the job. He has worked on Williams pipes in the past. 3/4 set seems to be the safe way to go. In my years of piping the one rule that I truly have always followed is, Don’t make adjustments that can be undone.
I agree with the Investment comment. I can assure you that this instrument will be played, a lot. However, my current situation is that unless my 2 month old decides to take on the pipes I will be selling this set in 6yrs to fund a new set. Which is the curiosity for the question at hand. Maybe a better question would have been, if you were to buy this set in 6yrs would you be more interested in it as a 3/4 or fullset? If this were to be my permanent set I would add the bass reg. and never look back!
I think I’d save my pennies and get an extra stock/bag when I wanted to add the bass reg. If I ever sold the set I’d offer the stock and bass reg as extra, sort of like some flute players have two headjoints.
But I’m sort of a preservationist, so …