That wasn't my suggestion but should work, too, with useful increased gate resistor. My suggestion was to install a series diode that cut's negative gate voltage.
As for the SCR current rating, we should have a rough estimation of coil inductance to estimate I²t. Without any inductance, you get I²t > 200 A²s, exceeding BT151 rating of 50 A²s by a multiple. A SCR in the 25 to 35 A class would be able to stand the discharge pulse even without series inductance.