try a spring reverb. maybe a little slap-back as well. introduce a horrible mid-range eq spike or two. anything that makes them sound less like real hands and more like '60s' hands is good news. the best ever hand clap sound i ever got was 10 years ago, with a cheapo AT 58 copy going direct into a 12-watt marshall solid-state amp with loads of reverb and through the headphone out into a cassette 4-track, levels a bit too high as well. couldn't even get close to that sound in a real studio with fancy valve gear and plate reverbs despite many attempts. i should have realised then that if it sounds good, it IS good!