if you want to gain power and new look and feel, change engine. take note that the cost of this would be higher than regular overhaul. why? tendency is once you have acquired your new engine (specially if surplus), you'll definitely overhaul it. not just overhaul, but blueprint it to factory specs if you have the manual.

if you want to maintain your original engine and want to save on cost, just do the regular overhaul. just be sure to have measurements made and compared with the manual. if you decide to take this route, there is a catch. be sure you still have a good block and head. if you have a cracked block, then proceed with the change engine. kung head lang naman, just get a surplus head and have it overhauled as well.