The T6A49A, exclusive to an early variant of the TI-81, behaves identically to the later T6A43 in most tests (see below for a difference). Here, I transplant the pin-compatible T6A49A to the TI-86, just because.
I later removed the yellow capacitor, and the overclock worked reliably.
If you look closely, I lifted one of the pads. Luckily, that was one of the four (!) unused pins. Probably should have practiced a bit more to not burn the board, but everything worked out nonetheless.

Functions that the T6A49A never carried out in the TI-81 do function on the TI-86
-Linking woks as usual
-With the backup battery, memory contents are retained after removing main batteries
-All ~96kb of user-accessible memory is usable as usual

I have yet to confirm that the low battery detection works. A set of batteries that triggered the low battery message in a TI-83+SE did not do the same in this TI-86.

BZ80TEST returns these results:
Test Version: 7
SLL Exists: 1
DAA Internal Carry: 1
MLT HL Missing: 1
RLD Uses A for Flags: 1
Flag b3 Settable: 1
Flag b5 Settable: 1
SCF/SCF AND b3/5 Set: 1
SCF/SCF AND b3/5 Clr: 1
NOP/SCF ORs Flag b3: 1
NOP/SCF ORs Flag b5: 0 <-- This would have been 1 with a T6A43
Undoc. NEG Works: 1
Interrupt Detect Bug: 1
Port $15 ASIC ID: 0
LCD Delay: 1
New Kinpo LCD: 0
LCD VRAM Width: 0
Port $14 Mirrors $04: 1

A variety of programs worked as expected:
-Finance and Inferential Stats packages
-TI-86 Demo
-pterodactyl (memory expander)

Things working pretty much as usual:

Someday I'll try this out again, but with the T6A49. Feel free to suggest any further tests Smile
Great experiment, thanks Smile
Great job, I'm happy to see some love for the older calcs. I'm also very impressed with your soldering skills Good Idea
For reference, here is the z80test result from my unmodded T6A43 TI-86.
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