Tim,
Occasionally, Mitchell parts and part numbers can be confusing.
Sometime after Garcia took over Mitchell reel servicing in the U.S., the part numbering system was changed. (It was rumored this was so Garcia could enter the part numbers into a computer.) Anyway, they went from the original Mitchell part numbers for service parts, which were two digits, to a new five digit system, with several exceptions. (The part numbering system was changed again, as time went on, but that's another story.)
The five digit part number, for a Mitchell 300 trip lever is #81020 as you mentioned. In the image below you can see that in 1971 they were using the new 5 digit part numbers, followed or sometimes preceded by, the old part number in parenthesis. (Could it be the service shops were getting confused?)
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- 1971 Mitchell 300-301-Parts list-My Collection-edited.jpg (190.72 KiB) Viewed 3797 times
So the old two digit part number, for the trip lever was #40 as shown above. The number #20 was given to a spool pawl screw on very early spools. (In time, the spool pawl design changed and the screw was eliminated, so that number #20 was dropped from part lists from then on.) Could it be that someone identified the trip lever #81020 as #20 leaving off the other digits?
Now, about the trip lever itself. The fourth version Mitchell 300 reel, was the first Mitchell 300 to have a full bail. Earlier Mitchell 300 reels had a half bail. The new full bail trip lever, with part number #40, was introduced. The design of this trip lever evolved over time, as did many of the Mitchell 300 parts. The first (full bail) trip lever was made of two components, the steel body and a steel rivet. The end of the trip lever body, that stuck outside the rotor, was saw toothed. This was done so that the user could release the bail manually, if needed, while in the bail was in the cocked position. To release the bail you were to use your fingernail to pull the trip lever away from the bail arm notch, thus releasing the bail.
The rivet which was attached to the other end of the trip lever was used to secure the end of the trip lever spring to the trip lever. (Shown in your photo above) Eventually the rivet was eliminated, thus reducing the number of components needed for the trip lever and saving $$$$.
Fast forward to newer later trip levers. Gone is the rivet, gone is the saw toothed end, and even the type of plating on the steel was changed. But, the new and improved versions were all engineered to be universal in design. By this, I mean that Mitchell decided that if you were to take a new and improved part and put it on an old reel, it would still work. It was this way for almost all parts that were sold as service parts. I don't know what part you got that wouldn't work but it must not be the correct trip lever for the reason I just explained.
Below, please see another schematic/parts list for a 5th version Mitchell reel. The design of the trip lever has not change much and you can use the list to help find parts if you ever need to.
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- 1956 Mitchell 300-Schematic and Part List-56 TradeCatlg-Resized.jpg (198.38 KiB) Viewed 3797 times
As far as baffle plates and trip levers, they were all designed to work together regardless of when they were made. I have not tried using old parts with new parts myself because as a collector I am more interested in the original correct parts. I guess the best answer I can give you regarding whether or not the two will work together is that they should.
Finding parts for the Mitchell 300 can usually be done on eBay. People even take apart the reels and sell the parts individually. I have spent many hours searching there, sometimes successfully sometime not.
Best of luck.
Kind Regards,
Bill