Vee's heater (removed as part of a restoration) cover removed, manky foam on top of the matrix ...
... and no foam at all on the other side, allowing a significant amount of cold air to bypass the matrix.
New seal fitted, seals the ends as well as the sides, so air can only pass through the heater unit by flowing through the matrix itself.
There is a flange at the bottom of the cover, which tucks under the main part of the case, that prevents the cover being removed with the heater in-situ. However, even if that flange were not there the cover would still have to levered forwards to clear the matrix ports as the lower part of the cover is a good inch down into the bulkhead cavity. It's been said a number of times that cutting the lower part of the cover off at about the position of the mounting flange that sits on top of the shelf (red arrows) would enable one to remove the cover easily and access the matrix. It does, but you still can't remove the matrix, as it's lower corner (yellow rectangle) goes right down to the bottom of the original cover, and hence is also a good inch down into the bulkhead cavity. The matrix slots into guides which means it can only be removed with a straight pull, it cannot be tilted so as to get the top corner out, then lifted to get the bottom corner out, without further modifications to the case. The only thing the cover mod allows you to do is fit an uprated impeller to the motor, which is said to be bigger than the hole in the cover, unlike the standard impeller.
Seal for the matrix ports where they pass through the cover. A grommet, so fitted to the cover before it is fitted over the ports.