Im also going to install a 54 235 into a 51 pickup.Am i corect that the 216 pump and fan will fit with proper clearence?

The 54 235 Chevy block used the same water pump as the 216.
Its a bolt in application with no modifications .
Installing a short shaft water pump on a 55-62 235 is a little trickier. Every one I have done have had their own unique problems. Best bet is to use the later [ late 50's] 4 bladed fan. These fans are just short enough to clear the harmonic balancer after installing the s.s water pump.
I also like to lower the radiator in its saddle a few inches since the 55-62 s.s water pump raises the location of the fan blade in realition to the radiator. I have had the best success with installing a 48-54 GMC radiator in the Chevy trucks that have been converted to a later 235. The GMC radiator fits inside the original Chevy radiator saddle & allows a lot of adjustment of the fan blade to radiator clearance. You can use the big 2 ton GMC radiator & still have room to adjust the clearance between the core & fan blade. I also like the look of the goose neck filler of the GMC radiators. The GMC radiators also come stock with a built in relief valve on the upper tank.