Who has done this, and what's the best way? I have an early Imperial and I laced it too loose. I don't have any pictures of the original Brooks lacing.

I did this using a variation of this (in black). It has a bit of give, and tension can be easily adjusted. I cannibalized the waist drawstring of a garment I found at Goodwill for mine.

They come laced. here's a pic I found:

I have 3x imperials plus 2 other self laced b17s and I lace them all tight as possible. For me it keeps the saddle sag minimal without requiring screw adjustment but I do like a stiffer saddle as they break in vs the side splaying/rubbing, etc. On imperials you can often lace them without support due to all the holes but on the self laced I use the seat clamps for better tightening leverage. Stock imperial lace is good, but also use a good round boot lace as well and prefer a traditional cross lace pattern.

Mine came laced like that too. Frankly, it didn't work that well for me, and I could tell that if I laced mine tightly enough, I would risk the stock lacing wearing into the leather. Hard to get a good shot with the saddle mounted, but hopefully this illustrates:




With this set-up, I can adjust the tension by pinching the spring release on the barrel, and either pulling in, or letting out tension to get it how I want, and then letting go of the barrel. The adjustment process takes about 3 seconds. Also, the cord is elastic, and it doesn't chew into the leather.