It's not a Nigel Gresley, that valve gear looks decidedly odd. You best bet on the boiler is to join a club whose boiler inspector is qualified for steel boilers. Probably as rare as hen's teeth. Te Southern Fed booklet http://modelengineeringwebsite.com/New_boiler_test_code.html refers.
I don't want to be too pessimistic, but without material certs and welder certs I wouldn't be too hopeful.