I agree, there is something different, the engine bay smaller? this is a Mk1 are they all the same? What I'm doing is working on the bench mockup, taking everything apart and installing it all inside the car to check things and taking it all back apart to go back on the mockup, thats why progress/photos are so far apart. I meant to take a photo the last time it was in the car, its so tight in there that 2D photos get confusing.I'm wondering if when you have the motor mount and chassis mount bolted on like that, they sit in the same position as they would in the car with the weight of the engine on them and flexing of the motor mounts. I believe the LAT chassis mount was modified more for clearance of the down-tube than clearance of the manifold itself.
Can you get a measurement from the outside of the chassis mount to the outside of the one on the other side and compare it to the dimension between the frame rails where they bolt in? I think it's possible it might be pulled in a little in your photo.
Here's a photo that shows the interference between the cast header and chassis mount, there is a large gap at the motormount to the chassis mount, I have another photo with a 3/8 bolt laying in there for scale. To get the motormount to seat onto the chassis mount I made the new chassis mount with just the 2 holes. Yes, that motormount is the old one and is slightly compressed and I have a new one to replace it but the difference between them is not significant.As far as I know that dimensions between the frame rails are the same. It's obviously very tight there. Even if the car had taken a hit at some point, it's hard to imagine the rails getting pinched in with the engine sitting between them acting as a brace.
Slightly off topic and not to suggest anything but there is a Tiger with a Boss 302 that was featured in one of the books years ago and has been on eBay recently and the description said the engine hangers were modified to bolt outside of the frame rails instead of inside to give more clearance. I haven't seen photos but it's an intriguing thought.