The cylinder bolts are to hold the casting in position - it is not a steam tight joint. There will be two pipes from the boiler providing the steam supply with nuts and joints accessed originally via the manhole in the front tubeplate - the standard arrangement for Aveling rollers and engines up to the turn of the century. The boiler would originally have been WI - whether it is now depends on whether it has been reboilered which it appears to have been given the manhole in the barrel. The cylinder cover is combined as two parts with a front cover to the valve chest - again standard for rollers and engines of that age.
Paul
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