Tim wrote,
A Taylor Jumbo like the 655 you're considering, or a GO 12-string will be the most direct analog for the Martin you had; those will probably have the most familiar feel when positioned in your lap. If I'm not mistaken, the GO has a slightly wider waist than the old Taylor Jumbos, so that may be a guiding factor in your final decision.
A while back I did some comparison measurements for 3 guitars I have. Within a little tolerance, I measured 3 guitar bodies externally at the edges, and did not account for any protusions from the actual bodies measured, to include bridge, strap post, or designed 'bellies' (Gibson J 200 specs actually show shallow arc for back of guitar).
The guitars I measured are Gibson J 200 Jumbo, Taylor 818e Grand Orchestra, and Taylor 355 12 string Jumbo. I posted most of these stats in multiple posts in thread:
http://www.unofficialtaylorguitarforum.com/index.php?topic=6050.30last post 2/14/16
* * *
Per request, I measured the waists and a couple more dimensions, all measured externally.
Here are length, upper bout, waist, lower bout, and depth.
818 is 20 1/2", 11 3/4", 10 7/16", 16 3/4", 4 3/4".
355 is 20 7/8", 12 1/8", 9 7/8", 17", 4 7/16".
J 200 is 20 15/16", 12 1/2", 10 1/4", 17", 4 7/8".
Couple of notes. Depth of 355 was re-measured to 4 7/16".
Taylor catalog shows 818 length at 20 5/8" and depth at 5".
Mine measured differently.
818e is still a big guitar, but slightly smaller than the jumbos. If I
had to guess, it would appear that the J 200 has the largest internal
volume. I don't have the capability to calculate that however. One of
my sons might be able to.
As to the other question, all of these fit comfortably on my thigh
playing in a sitting position. I am of average height and weight and
mostly play seated.
* * *
You got me thinking about low on the knee, so I did a little more
measuring. Just as baseball has WAR (wins above replacement), I now
have SAW (strings above waist). This would be the distance measured
from the treble e string perpendicularly to the nearest point on the
waist. Turns out that distance is a hair over 4 1/8" on both my 818e
and J200. This means that my seating posture/position is the same for
each guitar. I've had the J200 for 30 years. No wonder that the 818e
felt right at home to me when I first played it.
* * *
New notes:
Depth is measured at bottom at deepest point.
SAW for 355 is a hair less than 3 7/8"
The purpose of the SAW is to give an idea of how a guitar should relatively feel from a seated position.
I have no knowledge of the dimensions of the Martin guitar that kleolotke referenced, but if you can obtain them, a valid comparison can be made. Best guess is that they are all in the same ballpark (concert hall?). I also don't have any measurements for an xx6 Grand Symphony for comparison. Hopefully this will be of some use.
Sorry if it's overkill.
Don