There is discussion about this the over at
Secret Project. Lots of charts on performance and various options.
Here's some info on a few unbuilt SENIOR CROWN variations:
SR-71I
30 September 1980 iteration:
-AWG-9 radar
-four AIM-54 missiles
-anti-AWACS tasked
1 November 1982 iteration:
-APG-65 radar
-four AIM-120 missiles (80 nm range when fired at Mach 3.1 and 80,000 feet)
-anti-AWACS tasked
-secondary anti-bomber tasking
SR-71(Bx) (1976)
-nuclear strike aircraft
-four AGM-69 missiles (514 nm downrange/200 nm crossrange range when fired at Mach 3 and 80,000 feet)