Work in progress...
Cheers Nick!
Thanks for your offer to help me out with my buttons. After looking at your pics though, I noticed that the buttons are completely different

Mine has/had the 2 square buttons and yours has the little round red ones. Our two cabs are completely different but I think the boards are the same... Yours is much nicer looking than mine btw (although the top on mine would look nice in my bathroom).
Now as for those pesky IC's...
I want to make sure that the ones you're looking for are in the right location on the board so I don't give you any wrong numbers. Few of them have any markings on them at all.
In location 19, there IS one which reads "LM3900n". That is 1 of 2 on the main board that has any ledgible markings left on it.
In location 1, the IC is marked: /905LM380N
So, if the one you're looking for isn't in location 1 or 19... then it's going to be blank or unreadable... at least on my board.
Now, I've also noticed that if you look really, REALLY close, all the ICs have different shapes stamped into them (a dot in the bottom left, 2 dots, or an oval shape with 1 dot). I found one burried down on the video board that has the same dot pattern (the oval shaped one with the one dot) as the one in location 7. It reads: 5N74367AN (I think) and is a Texas Instruments part. Since they have the same dot pattern, maybe they are the same?
Let me know if that helped. If not, I'll be glad to go in there and check out any other locations on the board for you.
-Beau