Yeah, cutting or notching this type of bolt jam is a last resort for me - you want to leave as much of the bolt intact as you can to work with. Using the Topec kit and an impact gun, I was able to at least separate the pump pieces and then later remove the bolts (which were loosened enough to rotate inside the bracket with the impact). Cutting/destroying the bolts before separation rarely leaves you with anything workable.
First, I let PB Blaster work on them a couple days, then used a torch to heat them and break up the corrosion a bit - this really only makes a minor difference, just enough to get it moving ...it's still gonna take some skill, patience, and a bit of luck. On the impeller housing, I had the bolt break off at the threads. So I welded a nut onto the other end and used a wrench to continue turning it all the way out the "backside." The other two were seized within the reverse bracket. The first, I was able to hammer it back the way it came in and then use a punch to continue it all the way out. The second one was more stubborn: I had to alternate: PB Blaster and heat several times, rotate it with the Topec tool, then hammer at it, repeat. At one point, the threaded side swelled from hammering, so I had to grind the diameter back down. It slowly started to back out and I kept repeating the steps. Eventually, I heated the bracket to try and get the hole to expand a little larger - while I was spinning it with the Topec tool, the threads caught on the corrosion inside and it backed out almost all the way. A few hits with the punch and it was free. I purchased all new bolts (M8 x 110) through BelMetric.com for about $3.25 each.