If you are low on budget then I would suggest overhaul current engine. Apart from regular rings piston and head work, ask your mechanic to surface head through proper machine, use single gasket, install new water body, install new balancer garari.
New kabli engine is a gambling or else you are smart enough to check engine life. Even then you will probably have to check valves and rings. Advantage with new healthy engine, you will have better gear box, better carburetor, better head. Disadvantages, paper work overhead, extra expense. If you are getting engine with auto gear box at 90K then expect 10 - 20K more on lubricants, labour charges.
Lastly I am not sure about auto gear box, its an old school technology, carby so you might not get a pleasure drive and economy but not sure someone else can shed more light on this.
Regards,
