Joseph,

A friend built my WM Cap for me and we installed an OS46AX with Bisson Pitts muffler.

Repositioning the engine mount is easy but must be done carefully. The idea is to keep the CRANKSHAFT's position or center line unchanged.

I suggest the following steps. Please read through before trying it. You might come up with a better idea.
1. Install the engine mount in the holes already provided.
2. At a later stage, you will need to remove the 4 bolts and rotate the engine mount to the side position. This is to be done as an entire unit, so apply a little CA to the engine mount so that it is a SOLID unit. A little CA should do the trick. DO NOT CA the mount to the firewall.
3. Once CA is dry, place the engine on the mount BUT with the engine facing backwards. DO NOT drill any holes on the mount to install the engine. Just use some tape to hold the engine to the mount.
4. Make sure the tip of the crankshaft touches the firewall and mark the position with a pencil. You will need to paste a piece of paper on the firewall hole. The mark indicates the center line of the crankshaft.
5. Now, with the engine still on the mount, remove the 4 bolts so that the mount (together with the engine) is free to rotate to the side position.
6. While rotating, keep the tip of the crankshaft on the mark.
7. Mark the position of the new holes.

That's it. New position with crankshaft center line unchanged.