tl;dr - I upgraded the heatsink on my Mk7...
I was having problems printing with the Safety Orange ABS using my T-o-M/Mk7.
By the time I got the toolhead up to the temperature I needed to extrude reliably on the hot end (225C) the cold end was getting too hot and the feed wheel was chewing into the filament stopping the extrusion half way through a print.
I tried upgrading the fan, and the z-axis but without effect. Plain ABS and Red/Blue both worked but I can extrude them at much lower temperatures.
Luckily I had some left over 2mm copper plate that I used to make the HBP.
So far, so good.
Made a sketch in OpenScad because things have to have a file that isn't an image... Perhaps it will be useful if someone makes this on a cnc.
Cut a rectangular section of copper plate 6cm x 5cm (to leave a border of 1cm on the sides and top.) I used a dremmel, remember to use oil or cutting fluid when cutting or drilling copper or Aluminium.
Center the Mk7 heatsink on the plate with the holes closest to one of the long edges. Mark the position of the bolt holes and drill 3mm holes.
Attach the heatsink to the copper plate using m3 bolts and drill out the hole for the stepper shaft with a 7mm drill using the heatsink as a template.
Cut some fins around the sides and top, grind out and rough edges and optionally polish/sand.
The nylon spacers will now be too long so shorten them by an appropriate amount and the reassemble the fan assembly fan->heatsink->copper plate->spacers and reassemble the extruder.