68-70 340 exhaust manifolds install question

Thanks, what do you mean "****** into the firewall"? A sledgehammer?
No, just using the floor jack/block of wood on the edge of the oil pan. All the way up like you are trying to change the motor mounts.

Leave the drivers side motor mount installed, but back a little torque off the nuts. This will allow the engine to tilt towards the drivers side, but prevent ripping the mount.

I also had to dent one side of my TTI head pipes. On the drivers side, closest to the subframe, I couldn’t get the bolt into the flange.