BITD, I got a 3 cog cluster for my S-A 3 speed, and fitted a cottered triple crank & still used the 1/8" chain it came with.
3 by 3 by 3 ... a 27 speed .. used 3 levers to change gear combinations.
will the spring tensioner be able to handle a jump from 46t to 32t?
thats 14 t.. same as most road doubles ,so a chain tensioner with 2 pulleys with a distance between the 2 pulleys like a regular RD
should be adequate.
you can always use an old MTB RD as a chain tensioner if you need more slack .