I assume stringer and stringing machine/method are the same right?
1. Try to put strings of thicker gauge on the less dense pattern and take it from there.
It is difficult to replicate the feeling for sure, but I guess this is the objective.
2. Once you are convinced (if you are convinced) that the thicker gauge works (do not jump to the conclusion that it will definitely make the racquet feel even more boardy - in fact, as other have mentioned, this might be caused by many parameters), experiment with slight differences in tension (close to your previous benchmark tension), but do increase the mains/crosses margin (say 3 pounds instead of 2 for starters).
This will help you sweeten/open the stringbed, increase pocketing and dwell time.
3. If you like the effect of this on the new racquet, you might want to walk that extra mile and experiment with an even softer co-poly for crosses, or with a spin friendly synthetic gut, before you do sth. extreme (and wrong) with the mains/crosses margin; 5 to 6 pounds is the maximum allowed difference, but it would be wise to factor in tension loss for different strings IMO and it gets complicated. I would never go further than 4 pounds.
3. Also I would really like to know what the previous (the 18x20) stick was and if how old it is.
* There are ways to make a new frame feel older (softer).
Nadal asks for that on his Aeropros sometimes. It is a procedure that involves a certain stringing process.
One reason why I love tennis is because it's a life lab. Really.
Last edited by Matchball; 11-29-2012 at 11:19 PM.