This Non O-A Visa differs from an O Visa in so much it requires validated Health Insurance from an accredited nominated Supplier AND a Police check. Which differs from a DBS Check in so much is will reveal not just a Live trace, to various indices but also to archive. So expect the conviction to be revealed. Drugs and violence convictions generally result in a failed application. However, yours is a long, long time ago. I suspect that you may be just interviewed at worse, or it may just be waved through. I wouldn’t be too unduly concerned. But whatever you do declare it.