So after lots of looking around I have still decided to go with the headway cells due to their value for money and capacity for weight. They are not the best but they are very good.
I purchased 2 battery packs pre-assembled by headway each pack is a 24S3P pack giving me approx 84 volts fully charged and 30Ah capacity. I bought them this way so I could get all the fixings and the Battery Management System (BMS) in one purchase. This means I have got 144 cells with all fittings to construct my final setup out of.
Note each cell with fittings are just under 150mm in length and 38mm in diameter. It is going to be a tight fit! I might not get all 144 in probably only 120.