Marc does use the Delta LF 12 in the BL / DRB 1260. The Delta LF has a bit more low frequency extension than the Deltalite II. The tradeoff is efficiency.
I have a BL1260 from 2004. It came with a Delta LF, which I have replaced with a Deltalite II. Although the Delta LF is rated to go lower than the Deltalite, the cab actually sounds fuller and bassier with the Deltalite.
Geni, you and I had this discussion when you were thinking of buying my 1260. I feel the Deltalite is an improvement over the Delta LF. The increased efficiency of the Deltalite makes the 1260 sound much fuller and deeper, as the woofer efficiency rating is equivalent to the mid driver rating. Since the Deltalite is nearly 3 dB more efficient than the Delta LF, it offsets the difference in power handling, since you don't have to turn up as much to get the same output.
One reason that Marc went to the additional midrange control for the DRB 1260 was to be able to tone down the midrange driver to better match the output of the Delta LF.
With the Deltalite, the lows and mids of the cabinet are much better balanced, and no mid control is needed.