There's a pin you insert through the passenger side engine flange, towards the transmission, into the flywheel that locks it at 90 degrees ATDC: VM.1089
https://millerspecialtools.spx.com/Detail.aspx?id=1312&gid=7Most use a 6mm allen if I recall correctly - the service manual actually describes it along with how to make sure it's aligned correctly. I picked up one on eBay (Miller Tool Man is a decent source), they're just over $10.
My opinion after seeing folks try things both ways is that unless you're a fairly adept mechanic, get the right tools and use them. You can get the cam lock tool and cam locking pins from GDE - put 'em on your Visa and all but $30 is refunded when you return them.
Peace of mind... not expensive.
Others have devised their own cam locking pins by grinding down bolts and either used similar cam locking tools or fab'd their own - both successfully and not.
Cost of failure - about $750 parts for new rockers & engine cover gasket along with the additional time and labor.
You decide.
Mark