I recently got my 4D56 engine overhauled, it was apparently blown. The sound is same as it was before overhauling (when it was in good condition, sound improves as engine running progresses). There is no issue at all in overhauling a 4d56 engine. The cost purely depends on the number of things you need to repair/ replace. Mine took around 1 lac but it also includes new radiator worth Rs. 8500 and a clutch/ pressure plate worth Rs. 9300 and brakes worth Rs.4100 and a new Head worth Rs24,000. I don't believe in engine swapping not at least with the same one until your engine has completely exploded (which I believe is not the case). If you know of a good mechanic and a good parts dealer (which normally people neglect, they depend on mechanic for parts) then engine overhaul is the best option. You know what you are putting in and what exactly is the condition of each and ever bolt. Visited shershah personally for a replacement head just 2 weeks back, trust me all the apparently shiny engine that they claim to be as good as new are not reliable at all. Checked four 4D56 engines for head, and they had minor cracks some where or the other. Hence, decided to replace the head with new one!