with a gas engine of that vintage the compressor is likely belt driven. If so you may want to loosen belt ant try spinning compressor by hand to make sure it isn't stuck. If you get the engine stated and the s -cams release but the shoes are still tight to the drum put it in reverse and GENTLY ease up on the clutch just enough to rock it and see if they will release. Do not do this if the s cams aren't releasing. Do it gently so that if they are bad stuck you don't tear the linings off the shoe. If useing a hammer try to remove dust covers and tap on side of shoe rather than downward on shoe or directly on drum as Koolkar said they are expensive. .After you get airpressure built up bleed the air tanks ( there should be petcocks on the airtanks) to remove any accumulated crud then build pressure and put air to your brakes it doesn't take much crud to cause a airvalve to stick some times.