a) I may not prefer the kabli one, because we can not be sure about its inner condition and it will also lead to change of engine no on the car papers, again anotehr hassle. I faced teh same issue and i decided to get the engine oevrhauled myself and thsi experience Alhamdilillah has proven to be very good. It was overhauled 1.5 ytears back and engine is [performing much better within city and on the long routes upto Sadiqabad and Rahim Yar khan with full time AC. You can imagine its performance the overhauled engine that it consumed about Rs 2000 CNG with AC from lahore to Sadiqabad.
Main benefit of engine overhaul is that i know that what is and what not in my car engine.
My total cost on engine overhaul was about 25K approx.
b) I changed the brake servo of my car with the Imported Toyota servo, changed the rear and front brake discs, full service of brakes and grinded the front brake rotors............... and now the brake is MashaAllah very very smooth and grippy. Servo was of RS 1700.
Best wished for your final decision and plan.