I've had to replace engine mounts a couple of times because I wasn't thinking and mounted the engine back on the mouts. Even a 1/8-1/4" moving the engine forward on the mout can have a big effect on the weight you need to add.

I also just did a neat trick on a waco bipe that was coming out tail heavy. The firewall is big and round, and the cowl had lots of empty space in it. So I bolted a second engine mount to the firewall, and mounted the lead to the end of the engine mount. That got it a good 2" in front of the firewall, and I needed less than half the lead in that more forward location. Obviously, I made darn sure the lead won't vibrate loose, if it does, it's the end of the plane.