On engines like mine, with plugs that have screw off/on tops and open (forked) wire ends, would you clip the wires onto the sparkplugs or unscrew the tops and put the wires under the nuts?
The holes in my wood firewall for the brackets at the bottom where they bolt to the frame rails are located so bolts that stick thru the firewall just barely hit, on the side, some body reinforcement wood so no nuts can be screwed on. What gives? Wrong firewall? Thanks.
Forked or not, I'd put the terminals under the nuts for a tight connection.
Without seeing them, I have no idea about the brackets and firewall.
And when tightening, turn the terminal just a hair CCW from where you want it to end up. Then, as you make that final little bit of a turn on the thumb nut, twist the terminal along with the nut, using it as a kind of "wrench" to help give it that extra little "Umpf" to keep it tight.