Hello,
My first suspicion would be that the "Ansa" brand exhaust may have some issues. Getting any clamp up system to install without issues is unusual but possible, as with Cees. At the factory the systems were welded at every connection except where the flanges are at the manifolds. Suspension load, condition of motor mounts and sub-frame mounts will all play a role in the final clearances of the exhaust parts under the car. It is a difficult and time consuming process to do it so no issues arise at the end.
The process I use is to first check to make sure the engine motor mounts and sub-frame mounts have not failed. Raise the car of the ground with the suspension "loaded" (weight of the car on the wheels). install all exhaust parts temporarily, using supports to hold components in exact position. Check hanger alignment, rubber bup stop at rear muffler, position of chrome tail pipes in relation to bumper and horizontalness, check clearance of rear muffler to the rear body panel, and rear fender bottom, check the clearances of the system at the rear suspension and points under the car. When everything is in position, I tack weld all the connections. Next I disconnect the system as a unit and drop it down far enough to solid weld every joint. Next, I bolt it back up into place. I also use a liberal amount of silicone seal at the flange connection along with new metal seal rings. The silicone seal act as a lubricant and allows the bolt connection to slide together nicely and improves the seal. Make sure to use new self locking nuts or you will be back under there again in the near future.
As you can see, with a clamp-up installation, you do ot have a lot of margin for error. But as Cees indicates a good fitting clamp-up installation is possible. I would also suggest using silicone seal at the clamp connections in this case. Position the clamps just at the end of the slots in the tubes.
A poor fitting exhaust, will rattle, bump and cause a host of vibrations and noises that will plague you for years. A good fitting exhaust will greatly improve the drive quality of the car. Take your time and do it right.
