Even the USA doesn't have block 60... as for J-11, the basic J-11 is just Su-27SK made in China, why want that old design?
J-11B is indigenous, but i think there are barriers - for one, the Russian won't be too pleased, J-11B used domestically in China is one thing, exporting it (with or without ToT) would creating even more political pressures. Of course there are going to be 10-fold increase for Indian members protesting on the forum, but if we can get the Russia's concern cleared, then other voices are irrelevant. There shouldn't be any obstacles on Chinese side, just a matter of how much aircraft they can produce...
Only one other thing, does Pakistan really need J-11B heavy fighter? Look at the need first, don't buy a 50in TV for a room when 42in will suffice.