How necessary are they? I had a hard time replicating the original. It’s drivable now, but at the same time, I don’t trust it. I assume the curves were there for a reason. This is on my 1997 S10 Blazer.
Nope. You need the coils to avoid metal fatigue. What you've done is fine-- the firewall is part of the body which is on rubber mounts while the module looks to be on the fender liner which moves with the frame.