Just a few thought on ratios: No matter what the final list looks like, the average ratio of DL/NW pilots will be approx. 7/5 or 1.4/1. With that fact in mind, it is just a matter of applying ratios within the combined list to reflect or equalize the underlying demographics.
My opinion only, but the most DL would plausibly compromise on the top of the list, which is 1.6/1 -which is the ratio of all WB pilots (DL/NW), would be a list constructed on strict (or nearly so) category positions. For example: 237 NW 747 capt./ 193 DL 777 capt. = 1.22/1 followed by 280 A330/181 767-400=1.54/1 for an average ratio of 517 NW/374 DL= 1.38/1. This, rather self-evidently, results in 517 NW pilots and 374 DL pilots in the top 891 positions at the combined airline. This ratio would address exactly the larger amount of flying NW brings in those.... (need I insert an adjective!?)...categories, as well as the greater short-term attrition at NW.
Looks good so far for NW, but that rationale and resulting favorable ratio at the top comes unavoidably, and ultimately -mathematically, at a price. To be technically correct, Delta has 639 captains in a wide body category that NW does not have, ie. 767ER. But let's ignore that, for the purposes of speculating on a compromise by DL, and follow the NW proposition that their 757 category should be treated as "equal" to the entire DL 767/757 category (intnl. & dom.) This would result in 1420 DL to 447 NW capt. which equals a 3.17/1 ratio -unavoidably, in DL's favor. Quite a "hit" for NW on that one, but it only reflects exactly, in terms of numbers of specific quality pilot jobs, what we each brought to the merger. (and does so rather compromisingly, equating the NW 757 narrowbody dom. to the DL 767ER widebody international)
As for the rest of the list, one can ratio various combinations of 737/A320/M88-90/DC-9 but overall the ratio would be close to 1202 (DL 737,M88) to 1039 (A320,DC-9) which equals 1.15/1 in DL's favor. All these category/ratio combinations average to the mathematically neccessary 7/5 ratio. Notice this smooth ratio toward the bottom of the list does away with the 400 NW pilot staple, to be replaced perhaps, by a fence containing that risk. Also, the the widebodies at the top would be fenced (but not the 767/757) for say, 5-8 yrs. I haven't by any means thought of all the contingencies, ie. aircraft deliveries/retirements etc. BTW, this proposal would result in a 2% relative loss of seniority for me.