Yes, the Titans are larger posts requiring drilling out the headstock. If your Slimlines are falling apart, there is a couple of things you can do to fix this. The covers are swaged on with 4 pins that are going through holes in the mounting plate. You can easily re-swage these, or alternatively, these can be modified to use small machine screws to hold it all together if desired. More work but more permanent, too. Do a search at the Rick Resource Forum for lots of info on this and, um, resources, of who can do the modding. I have a set that have been modded, on my March '73 4001, and they are really nice now.
If you want to replace the tuners with something different, I'd suggest Hipshot Ultralite tuners with their cloverleaf keys, or the Y keys for something more modern looking, like those on my former July '73 4001, that a friend has, now. They required only a bit of reaming to get the posts to fit. Another possibility is the Hipshot HB_5 tuning keys; their posts should fit with no modifying, but again, check that the tuners won't overhang the headstock.