The Swissair plane had CF6-50C2B engines, the United plane had CF6-50C2 engines. The -30 aircraft had a large range of CF6 engines on them including the -50C, -50C1, -50C2, -50C2B, and -50C2R. Each varied a little in thrust available, time limits on max thrust etc. Some of the engine exterior was changed between the sub-types, which explains the difference in appearance in the photographs.
By the way, the Swissair aircraft is now flying for Northwest as N226NW. The United plane was converted to a freighter, and was one of the last DC-10's they flew. It has been in storage since February of last year.
One smooth landing is skill. Two in a row is luck. Three in a row and someone is lying.