if you can get a 575 thats the way to go .while the d104m6b is a good mic and i have used them for years ,i get tired of the key issues.seems they only last maybe a year then the key gets scratchy ad no matter how many times you clean it ,it returns in short order.
i never had a 575 with that problem ,and the keyer is much longer on the 575 and makes it easier to hold a key .holding that little button in on the m6b can get tiring .
other than those issues they are good mics ,but i try to get good 575`s now
good luck man ..i know what you mean about the older ones ..those are the ones i would always buy too.
i think you might mean the tmd107,those are engraved ,but they take a 7 volt round battery.