If you are asking if a short shaft water pump for a 1959 235 will work on a 1959 261, the answer is yes.

I know you did not ask, Terence, but I would like to suggest that you consider using a 1948 water pump with an adapter plate to fit the 1959 261. This will place the water pump in a better location relative to the middle of your radiator.

Jim Carter sells these plates and they can be bought on eBay (search eBay for "235 pump adapter").

http://shop.ebay.com/items/_W0QQ_nkwZ235Q20pumpQ20adapterQQ_armrsZ1QQ_fromZR40QQ_mdoZ

Be sure to ask for installation instructions. I bought a plate from Jim Carter and from the eBay seller - neither one sent instructions. Jim Carter emailed them immediately, after I asked for them. They were very good instructions, EXCEPT in the case of suggesting that seals/gaskets were not needed. Use seals/gaskets on both sides of the plate.

Tim

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.