I got my engine for 100 , and it came with a crappy frame!
I think you should get a newish engine, open her up, do the triple bypass, and call it good.
Find a good motor for $100 to $200 max. If it is a parts bike OK.
I would imagine with the effort you have some emotional attachment to the current bike.
I bought a CB550 and have more than $500 and I'm just now turning attentions to the front brake system.
Needs new lines and a caliper rebuild. MC has been rebuilt...
BTW, if you paint the MC use the brake caliper paint and while it's apart bake the painted MC so it is fully cured. Result is a brake fluid resistant coating.
I knew I bought a project bike and I knew I would have more in it than if I spent $1200 on a good running one.
My patience wasn't deep enough for the saving $1200 and I wanted a project as stress relief. I don't work on it when I'm upset.
I have another bike I can take on a ride if I want to have a stress relief... Or I go to the arcade or range and put little holes in paper targets.
$235 on Bridgestone BT45 Battlax tires (165), mounted & balanced ($50), new rim strips ($2), new IRC tubes ($18) (I think spending money on tires is a life saving investment and want excellent traction in wet and dry...)
$70 on a set of better rims as the spokes and chrome rims were not so nice on mine...
$30 newer better condition seat
$60 carb rebuild kits
$30 rear grab bar and signals
$65 engine guards for the cases
$40 points & condensors
$40 MC rebuild kit and hone
$35 new ignition & seat lock
$45 new speedo & tach as mine were seized
$75 new braided lines
$170 ($85/ea) drilled & surfaced dual rotors
$25 new plugs and plug caps
$50 rustoleum paint job
So, if I faced a engine problem I would not hesitate to change it.