Quick (and happy) update. Belt(s) delivered, popped one in some hot water, and "walked" onto the big pulley turning the engine with a 22mm deep socket following some advice. All went on not too bad. Started, pressure built as cranking, then straight up to 60psi on start up. Seemingly, no untoward noises, rattles, clatters or bangs so fingers crossed, a lucky escape (though didn't get chance to take it for a drive). Thanks all for your guidance, advice & words of encouragement