I'm not going to go through the whole installation. Big Bike Parts includes a copy of the installation instructions with the set of switch housings. Unfortunately, these don't really match a 1500 Drifter, so use as appropriate.
The clutch side installs just as you would expect with no surprises. There is a spring for the horn switch that is a bit tricky to get back into place, but the install is easy enough. The knob for the turn signals pops off the stem. Everything goes back nicely.
The brake side is where things get tricky.
The cable tensioner guides fit up inside the old housing but the new housing has one whole too small and one hole is threaded and too small. So I had to put both halves into the drill press and drill out the holes to fit the tensioner guide. These are very soft so it was very easy to drill.
Also, the edges on the tenion that goes into the hole on the handlebar needs to be smoothed to fit more easily. All of the edges of where the switches pass through are tight a little smoothing wouldn't hurt.
Inside there is a black plastic plate/cover. When I reinstalled that, only one screw was long enough. I only used one screw as a result. Apparently the housing isn't built quite right in that area.
And, lastly where the housing mates with the bars could use a little smoothing. It is a very tight fit. I stripped the head of the phillips M5x25 screw trying to get the housings to seal properly. I finally had to get some allen head screws to get enough leverage to get it right.
So, this was a relatively easy install as Drifter installs go.
COMPLEXITY RATING (1=EASY; 10=EXPERT): 4