Fonsini,
If you assume this would require a vertical take off, which it might not:
From memory an average 107, on an average day with tanks and ASW - but nothing else would give you a VTO of siro three thousand pounds of fluids (to include 500 pounds of water). So you would have siro 2000 pounds above MLA or 1300 before you needed to consider landing.
From memory that would give you 10 or so minutes at low level at 420 kts, so I'm going to go for 'about 70nm'.
However, I do recall the T12A had significant CoG limitations which were complex and would probably have impacted your ability to VL, VTO, transit and then VL again...one of those may well have been out of limits.