You do no better at this point in time to make reference to Issue 28 of Byways of Steam by Eveleigh Press. (Recently released and still readily available)
Feature article is the Loco Depots of Narrabri West and Moree by Ray Love, many photos of the 27 class working in the northwest and a small appendix article detailing the 27 class locos themselves from PWD thru to Preservation, am willing to stand corrected but pictures of their original tenders are included.
Hope this helps,
There is one photo in the book showing 2708 outside Eveliegh shops, the caption says the tender is as per original fitted, being a unique style including bogies, it is of the same type that is shown by 1210_5810.
From what I can see of that photo, & the one in Byways, I would suggest its almost a hybrid type somewhere between some of the Baldwyn tenders that has solid plated hungry boards as seen on some of them. Likewise the rivet line along the side of the tender which shows the angle of the coal plate, is also distinctly different to that of a D50/3650gal tender. Likewise the bogies under that tender are similar to those of the Baldwyn tenders, but the main frame appears different.
Give that the 27cl came into NSWGR ownership I would doubt very much that the original tenders would have been modified to the extent that would convert an original tender into that of a more standard D50 type, given that many of those tenders had become surplus over the years with the Wampu, & later Turret tenders being available.
Remember that the 53, & early 55cl arrived with new built 3650 tenders which were in many cases replaced with the newer Wampu which made them spare. Rather than a rebuild or conversion they would have simply replaced the originals as they became life expired.