Thanks for the link on how to drill evenly spaced holes. I'll probably add those to the top .
To start I drilled 5/32nd holes between each heat sink fin on the bottom and top of the chassis and also a row on the top of the chassis back.
Putting rubber washers on the transformer mounting screws and a thin layer of rubber on the bottom of the unit allowed me to test fit the chassis top on with no issues.
I was wondering if having the large caps on the Antipole where they are so close to touching the chassis bottom is a potential issue/problem ? The Antipole just fits on the partition height wise or I would have raised it . When I got the NABU surplus case I grabbed a sheet of amplifier isolation rubber for a buck so I could add that if needed.
I soldered the chip to the PCB after lining it up on a flat surface with the heat sink but now I wonder if my wood workbench top wasn't perfectly flat as the chip in the case only matches up to the sink on the top third. The chip isn't perfectly perpendicular to the sink surface or I drilled and tapped the mounting hole at a slight angle.
Might have to desolder and raise the sink with a sheet of something so the mounting screw for the chip lines up properly.
It looks like there is a gap between the HS and the PCB which would indicate the chip is tipped outward at the top.
You can try bending the chip slightly back in vertical alignment. However, the hole you drilled and tapped in the Heat Sink (HS) may also be out of alignment or drilled at an angle as you mentioned. This could pull the chip outward at the top.
I would take the board and HS out of the chassis, and set it on a known flat surface such as glass or a piece of MDF. Use a combination square to check if the chip is perpendicular to the board. If it's not, try bending it into alignment then check that the the tapped hole is perfectly centered. If the hole is off, flip the HS over, and drill/tap a new hole.
A good way to make a perfect tapped hole is use a drill dress to drill the hole, and use the drill press to tap the hole by inserting the tap in the drill press chuck, and turning the chuck by hand, not under power. This keeps the tapped hole perpendicular.
If bending the chip perpendicular with the board creates a gap between the chip and the heat sink when the HS is pressed tightly to the board, it would indicate that the chip was installed with the straight legs set deeper than the bent legs during soldering. This would make the top of the chip contact the HS, but not the bottom of the chip. The solution would be de-soldering the straight legs only of the chip, and lifting it into perpendicular alignment.
Something else to consider is anchoring the HS to the chassis. The reason being, the heat sink is a little top heavy, and could tip, and bend the chip possibly damaging it if the chassis was carried on its side. With my latest build I am going to drill/tap the thick section of the HS, and screw it directly to the bottom of the chassis.