Is it possible to upgrade an old F-16 to the Block-60/62 standard?
F-16D/E Block-60 is an evolutionary upgrade to the F-16A/B Block-15 with the following differences:


Engine: General Electric F110-GE-132 in place of Pratt &amp; Whitney F100-PW-200 turbofan.
Avionics: This is where the majority of upgrades have been carried out. Block 60 has the AN/APG-80 'Agile Beam' AESA radar, AN/ASQ-28 IFTS (Internal FLIR and Targeting System) replacing the earlier external pods, ALQ-165 electronic countermeasures system, improved pilot displays, improved mission computer and ability to fire more weapons like AIM-132 and AGM-154.
The main structural modification is the addition of conformal fuel tanks in the wings, with slight change in dimensions and increase in MTO weight- 46,000lb vs 37,500 lb




F-16 Block 20, Image from f-16.net



F-16 Block 60, Image from f-16.net

Though it is possible to upgrade block 15 to block 60 (albeit with some heavy modifications), the question is why anyone one would do that. Even the youngest Block 15 aircraft is nearly 20 years old (the last aircraft rolled off the assembly line in 1996) and LM has shut down the F-16 production line. The upgrade will be costly (you're changing some of the costliest items in the aircraft- avionics and engines) and will not be cost-effective in an aircraft past half its service life. Also, as far as I know LM doesn't offer any upgrades from Block 15 to 60, indicating consumer indifference.