For transferring the marks. What I just did was make a second spacer and counter sunk one side of it. This allowed me to mount the spacer to the stand offs and have the one side still flush. Then I enlarged the center whole on the firewall and used small clamps to now hold the engine in place (with the standoffs and spacer). Now align the engine (which takes some time of putting the cowl on and off making slight adjustments each time. When done - take cowl off trace around the spacers I made, take engine off and spacers off from the standoffs. Then place the spacers back on the fire wall and clamp back on, and just drill out the wholes. Works great.

Best of luck
Brian
If any questions email me and I will get some pics