Hi Mike
It is possible to remove the front roller on the keel with the keel supported I suggest in its highest position. It does just clear the roller on full lift. However if at all possible it might be easier to jet wash out any barnacles and scrape out the housing, again with the keel right up and supported rather than strip this out.
Some suggest grease on the roller, others prefer a PTFE spray or just make certain it is clean enough to rotate and leave it 'dry'
If you do go ahead, the two screws are visible in the alloy plate but will probably be difficult to turn, there are usually captive nuts to deal with inside the housing and by this time these may have corroded onto the stainless steel screws. Using a socket set with a flat blade screwdriver socket, might give you enough leverage to ease the screws out, but they are, from memory, only 6 mm !
Hope this is some help.