My 15" shaft 2005 Mercury 5 hp single cylinder 2 stroke weighs 43 lbs.
It has forward neutral and reverse. It has an integral fuel tank as well as a snap on fitting for a remote tank.
Its primary function is as my emergency kicker motor on my 22 cruiser.
My non adjustable mount has 4" of setback from the transom.
With the 4" setback and a little help from the offset from the center, the 15" motor does well on the 20 transom and in the tilt position clears the water when on plane with the big motor. 3/4 throttle cruise on the heavily loaded 22 cruiser is 4 mph. Reverse is acceptable. I have a snap on steering tube that allows me to partially tilt the big motor and steer from the helm.
I keep the integral tank full and ready to go with premix.
In a total failure of the big motor where I may have to go for several days on the kicker, I plan to add oil to one of my main tanks to the proper mix ratio and snap the fuel line directly to the kicker.
This set up works well on my 22 and would do a stellar job on your 16,
Properly set up the 15" motors work well, are more readily available, and will function better on a wide variety of canoes, dingys, inflatables and other small craft than a 20" shaft motor. The short shaft (15") motors are also more compact. lighter, easier to move and store than the longer shaft motors/
There are several photos of this installation of the short shaft (15") kicker with the set back bracket on my 20 transom in the Bixby's Cub Photo album.
Also of this vintage are the Mercury 2.5 and 3.5 2 stroke Motors with a weight of 28 lbs.
I have owned both and they are good motors, simple, dependable and easy to work on and should push the 16 well.
But Forward and neutral only, reverse by spinning the motor 180 degrees.
Integral fuel tank, no factory aux fuel tank fitting, but would not be hard to add a tee and install the aux fuel fitting if you thought you needed it.
I have spent time on a friends 16 and every few pounds seems to matter.
I would consider the 2.5 or 3.5, 28 lb Merc short shaft (15") 2 stroke as your best option. Keep it simple, lock the little motor on center and steer from the helm with the big motor as a tiller on long stretches. and move to the back of the boat and steer the little motor directly when maneuvering.
Try it first just clamped to the transom and if you are not happy with the performance get a mount with a few inches of set back. The set back allows better water flow to the shorter shaft motor.
I would have no qualms mounting a well cared for vintage lightweight 2 stroke as a kicker motor.
Best of luck