Eventually, I drew this mission for my own and did the usual mission prep in finding all that I could about it. I came across this particular entry in http://eve-survival.org/wikka.php?wakka=Vengeance4gu:
Rachen Mysuna have 50km orbit range and 75% chace for shield boost (1000hp each 10 seconds) so low SP BS pilots can have problems breaking his tank. Rachen's 25% chance for defender doesn't help either.That first try didn't turn out so well. The rest of the mission was as easy as level 4's get. But Rachen was a tough nut to crack on my own so I had to call for backup myself from a kindly corp-mate. I would eventually get this mission again several times and I would have to refuse my agent every time. I think that bastard actually enjoyed watching me squirm while I did the mental computations on whether it was feasible this time or not.
So, today, he once again offered Vengeance to me with a slight smirk. Only this time, I surprised him by accepting it. Since that first time, several things had changed that I felt would give me a good chance at soloing Rachen. First, there was my full rack of Arbalests. I also had trained up to 5 tech II medium drones and level III of Drone Interfacing. I had also gotten some DPS implants and I had finally been able to fit in the third Ballistic Control System II into my setup.
This time was a bit closer but I still needed just a little more oomph. So I went back to my mission base and traded in some loyalty points and isk for Caldari Navy Wrath Cruise Missiles. Warping back, I found myself about 30km from Rachen Mysuna. Rather than keep my distance from him like last time, I strove to close in and reduce the flight time of my missiles. He folded so easily I couldn't believe it. The missiles didn't do that much more damage. I suspect that the short range played havoc with his Defender missiles and that was the reason for my solo victory. Either way, it was still a sterling vindication of how far my DPS had come from that first try.