At 40A/us that thing is going to take an eternity to reach peak current! Are you sure it can even handle that, thermally*?
*Probably. I mean, SCRs are rated for a shitton of abuse, they have fusing ratings after all. I'm still not sure what you'd do with milliseconds of surge though. Unless that's exactly what you're doing, a 10/1000us surge generator for example, ah, but even then the dI/dt isn't anywhere near that.
To trigger the SCRs I am using this helpful guide by Semikron. I am currently using a capacitor discharged into a pulse transformer which in turn is connected to the scr gate. The pdf also has great information on choosing a RC snubber for protection.
If you need more sustained drive, consider using AC excitation. Pretty standard approach for phase control and inverter application. The SCR won't much care about mild reverse bias once it's conducting, and the main penalty is a ~Fclk jitter as far as when it finally turns on (which if it was reverse biased previously, isn't going to matter, you'll hardly notice the anode voltage rise in that time).
Shouldn't be very important to pulsed applications though. Just FYI.
Tim