Ask Hypro marine in UK,
you can swap Latham reservoir to seastar reservoir,
SEASTAR SOLUTIONS SeaStar Hydraulic Steering Reservoir with Relief Valve | West Marine
ask the following reference for the reservoir and for the relief valve.
Mfg # HP5860HY
Model # 12785218
By the way, it's a complicated system, and not the cheapest way for steering.
most people use capilano pump as a return line to the pump is installed.
You need to check if the 2.4 seastar pump has a removable plug, where you can adapt the return line. (per latham drawing).
usually there are four 1/4 NPT port on the rear of pump, check if one is avalable for return line.
Hypro marine can confim you that, and if the total installation price doesn't goes to the sky.