Well the 24,500 lb J-75 was about as far as you could go in the 1960s. If your Israeli upgrade can wait until the 1980s, then you can get F-100s and F-110s in the 27,000-30,000 lb range. A more exotic option might be the Volvo RM8 from the Viggen which produced 28,000 lb, but I doubt whether Volvo would get an export licence for Israel from the Swedish government. However, since it's basically a P&W JT8D with a Volvo afterburner, it might be possible for P&W to buy the rights to make the afterburners themselves.