im going to pull an RTFM on you.

this is from my XDF notes explaining the parameter, which you'd see if you hover your mouse over the item in the list:

This table allows trimming of individual cylinder AFR calculations. It is a multiplier, increasing it richens the mixture. Obviously 1 means trim is disabled for that cyl.

Some people have had success using infared measurements to tune these values.
also from my writeup on fbodytech.com:

http://fbodytech.com/tuning.html#idle

and solomon's website:

This table alters how each cylinder is fine-tuned based off the calculated fueling needs for each bank. A number below one leans out the cylinder, and a number higher than 1 richens it up.

The ideal way to tune this table is to use an IR thermometer to measure temperature at each cylinder exit and to use the results to tune each cylinder's trim until the temp readings all closely match. It is best to start with all cylinders at 1.00, and first have the BLMs close to 128 from VE/MAF sensor table tuning.

Generally, the middle cylinders (3-6, especially 3-4) will require the least tuning, so use their temperatures as the baseline.

It has been shown through practice that a leaner fuel mixture increases combustion temperature, and therefore a richer mixture decreases temperature. You can use this logic in reverse: cylinders reading hotter than the middle ones should have their trims increased (ex. 1.01), and cooler cylinders should be lessened (ex. 0.99). Start with 0.01 increments until you see how much the temperature is affected.

However, if a cylinder is severely starved of fuel, the temperature can actually read much lower from lack of combustion. This can happen with the two front cylinders, so if there is a major difference between some, with one or more reading much lower (over a couple hundred degrees Fahrenheit), then you should consider adding fuel to those first.

Obviously, this method is best done at idle. But, there are two tables, one for idle and one for off-idle.

For off-idle, without a dyno, with the car in park you could set the throttle to about 20% (with a stick on the pedal, or someone else holding it down), and then measure; or, for tuning while the car is moving, install EGT sensors into each cylinder exit point on aftermarket headers, and either be able to log their readings or have someone in the car with you doing it.

Tuning this table can also solve BLM splits, where one side of the engine is either richer or leaner than the other side (i.e., 126 for the left, 110 for the right). Having such a condition will reduce power and MPG and could cause a dangerous lean condition for one side or cylinder depending on how bad the split is.
anyway that project is looking really slick so far!

i wouldn't actually play with your tune much more without some driving datalogs, with one exception, how much is it going to weigh? i may have gone a bit far in your timing advance for something heavier like that.