If its more a loud ticking then actual knock like lower end bearing issue or maybe broken piston skirt resulitng in excessive psito to cyl clearance/piston slap then it could simply be a bad/collapsed hyd lifter,dirt in lifter from change to full syn with maybe more detergent loosening up some gunk that got into a lifter collapsing it, or there's enough wear now with over 40k miles on the motor that it could use a valve adj because the lifter plunger is at top of its travel and cant take up any more clearacne thats present due to normal wear over 40k miles and is making noise.

Have the mechanic chk those itmes out 1st before bothering to go for full top end rbld when it may not need it.

It better to spend A $100-$150 to chk that out 1st with a simple valve adj then do a full top end rbld for $1k-$1500 just to find out after that it still makes the noise post top end rbld due to a bad/collaped lifter or lifter that may have dirt/debries in it.

And BTW flat tappet cam'd motor need zddp/zinc & phos that todays mobil 20-50 pass car oil doesnt have if thats the 20-50 mobil you used.

But if you used the mobile bike 20-50 your fine,it will have the zddp.

Also,the mobile 1 pass car hi perf 15w-50 oil does have enough zddp for the flat tappet cam in your bike if you want to run that because its little cheaper then the bike mobile 1.

Scott