I am building another project which has a triumph 6 cylinder engine. The engine mounts are angled rubber bush mounts, about 30 degrees from vertical

I am at the point of welding the engine mount brackets to the chassis. If I just jig them in situ, when the engine is installed the weight (which is a lot) of the engine will put a shear load on the mounts and push them out of alignment. Any engine movement will put an excessive shear load on the mounts.

Presumably the right thing to do is to move the mounts inwards so that when the weight of the engine is applied the mounts come back into alignment so any movement is transmitted perpendicular to the mount. Is that right? .... and if so how do I work it out?

For angled mounts, I'd have slotted holes. Weld them with the mounts at the top of the holes and then once settled, the mounts should be further down the slot if that makes sense?!

I have the same thing planned with my MX5 engine, it's mounts are at 45 degrees. I'm planning on fixing them to the engine, then dropping the engine in place to see where the mounts settle. Then mark them up, lose the engine and get everything fixed in the right place.

Slotted holes are the normal way of doing it

OK, I suppose that's right. I can see it would work if the mounts are flat bottomed and the bolts just clamp them up when they have reached their working position. On the Triumph mounts the mating flanges are vertical and the bolts pass through horizontally so the weight of the engine sits on the bolts in shear.

I just question whether the tension in the rubber would be sufficient to overcome the friction in the bolts. I suppose I can always push them down the slot until the rubber bushings are in alignment.

Thanks for all your advice, I will give it a try