Just adding some little fact, why MiG-25 will never ever ever touched the SR-71 - As many of you knows very well, MiG's Tumansky R-15B turbojets are redlined at mach 2.8, while the SR-71, with its Pratt & whitney J58 'turbojet-with-compressor-bleed-bypass' is capable of sustained mach 3+ flight - And service ceiling of MiG-25 is far below service ceiling of SR-71 (as far as 5200 m if carrying four missiles), so diving to gain some airspeed is impossible - MiG's Smerch-A radar has enormous power that enough to 'burn' through enemy bombers jamming system, But i'm not sure it can burn through SR-71's jamming system
Good luck; SR-71 still has about a third of the speed of sound on that thing, AND it's a Stealth Aircraft, so radar-guided missiles wouldn't be the best idea.
Exactly my point; the MiG would have a hard-time intercepting the Blackbird unless it somehow got really close, or above it to gain speed while diving.