Wiki, citing Burke 2010, says:
Costs continued to rise, which led to concerns at both company and government upper management levels, and the aircraft was also falling short of many of the requirements laid out in OR.343, such as takeoff distance and combat radius. As a cost-saving measure, a reduced specification was agreed upon, notably reductions in combat radius to 650 nmi (1,200 km), the top speed to Mach 1.75 and takeoff run up increased from 600 to 1,000 yards (550 to 910 m).
BTW Viggens mentioned proved to have excellent short field performance.
Wiki also says Viggens they had no problem locking SR71s.
Swedish JA 37 Viggen fighter pilots, using the predictable patterns of Lockheed SR-71 Blackbird routine flights over the Baltic Sea, managed to lock their radar on the SR-71 on numerous occasions. Despite heavy jamming from the SR-71, target illumination was maintained by feeding target location from ground-based radars to the fire-control computer in the Viggen. The most common site for the lock-on to occur was the thin stretch of international airspace between Öland and Gotland that the SR-71 used on the return flight. The Viggen is the only aircraft to this day to get a radar lock on the SR-71.[26]
The last statement is unlikely IMO. The huge FoxHound radars should also have had a good chance IMO..