1) MOSFET model: I'll try to follow this advice.
2) The Injector is a Delphi EJBR02101 Z, common in Euroland.
Its interesting you say 50 v. When these are bench tested, for servicing, 12 v is the norm. We found we needed 15 v or more with our home made circuit - this before there was the info available (Industrial Secret?) that is available now. Because there were several transistors in play, the final voltage would have been about 13 v. But it needed that, the way we had it.
It worked fine but maybe not most power-lean. As told above, we seek a new better circuit owing to creeping unreliability.
And we were using the coil between the + 15 v and ground. As advised above, it will be with better FETs. Thank you!