If you have not already mounted the rudder, don't! Stand the plane on it's tail, secured to something that prevents it from falling over. Tape it to a table or run a line around it to sercure it to something.

This presumes that you've already determined what length of standoffs you will need to bring the face of the prop hub outside the cowl and have them made up already. Now simply set your engine on the firewall, slide the cowl over the engine, and move the engine around a little until it's where it needs to be.

There's some instructions on the Wild Hare website that will help you out. Probably some pics as well that you can download for assistance.