Won’t hurt to try it mate although if your lifters are gone the only real fix is replacing them, nulon lifter free is the additive you wanna use also have you cleaned the afm lifter screen thing under the oil pressure sensor?
You do realise theres a heck of a lot more to it then simply dropping in a manual transmission don’t you? There’s a lot of things that have to be changed to make it all work seriously you’d be better off selling yours and buying a manual car
Can’t help with the tail shaft question but the std manual diff ratio is 3.45 I’d think your auto diff will be 2.92 and you could go to something like a 3.9 if you want more response also I’d think you would need the manual ecu for your conversion? Could be wrong on that and you’ll probably need...
In my case it had only come away at the back a little bit so I just used some spray adhesive that I already had to glue it back up and seems to be holding well so no need to get it done just yet but will one day