I think of converters like slipper clutches, in that they allow the engine to work in the RPM range where it makes good power. As-a-mater-a-fact you can look at where the converter flashes at [ where the RPM drops to right after the shift] which shows the true stall, to see if any of your combination changes causes the converter to flash at a higher RPM. Again, like a slipper clutch, the more power [ torque] you make the more the clutch [ stall] will slip.
OK, so you ask where do you start to pick a converter to work with your motor ? What all the converter companies want to see is dyno charts, because it will show them what your motor is doing. If you don't have or can't get some dyno pulls, I think you should start by talking to your cam guy as to what RPM range is your motor going to run in. As an example if you have a 6200 stall converter, BUT your motor comes on at 6500, it will struggle for 300 rpm. Second choice of how to give the converter company good info is a computer data system, ie RacePak, RPM, so they can see your RPM chart.
It seems all the fast JrFuel teams are using 7" A-1 converters, also most Comp Elim teams. Coan looks like the second popular converters. Now your 526 I'm sure makes more torque than our 10,000 RPM 400 ci motors, so you may need a 8" converter, a few Heritage A/FD [ blown alky] guys are running 9".
I highly recommend calling A-1 Performance, 360-574-9966 to see what they would recommend for your combo. Don't get confused by what other types of race cars use, their combos may not be like yours. IE a Super Comp, Super Gas, 3,000 door cars need different converters. Hughes seems to be popular in Super Comp.
Now what I did because I didn't have any dyno runs,to get to a few converters to work with my JF was to buy a second converter that I told A-1 to build 200 rpm looser than what I had, run the new one, if the car ran better, I than sent the old converter to A-1 and told them to build it 200 rpm looser than my new one. If that ran better than I sent the converter I took out to A-1 to make that one 200 rpm looser, etc until it did not improve. Then I worked on the motor. Now the real smart, but not cheap, option is to get one of the new 2 pc alum converters, so you can take it apart at the track and change stator to change your flash rpm. I have 5 steel converters now that I use with two different type motors, SBC, and early Hemi. But if the 2 pc alum converters were around when I started, I would not have a trailer full of converters, just stators.
Bottom line is you need to get good info to the converter manufacture.
Feel free to call me with any questions, 805-444-4489
Jon