The original manuscript is not extant here, but there is definitely room for done in the spacing between extant portions. The 1905 LDS Chicago edition accidentally deleted the done in this passage. The subsequent 1911 LDS Chicago edition followed this shorter reading since the copytext for that edition derived from the third corrected printing (in 1907) of the 1905 edition. The 1920 LDS edition restored the original done.
Elsewhere in the text, there are five other occurrences of done according (where done is a past participle):
The expression “it would have been according to the fulfilling of his word” is not impossible, as in the following example: “and all things that he spake hath been and shall be / even according to the words which he spake” (3 Nephi 23:3). So either reading is theoretically possible here in Alma 60:16. Of course, the critical text will maintain the done of the earliest textual sources.
Summary: Retain done in Alma 60:16, the reading of the earliest extant text: “for it would have been done according to the fulfilling of his word”.