As a wise man on my tractor forum told me - if you have gas and spark in time it has to run.
You said you put gas in the cylinders not the carb. ? Why that way? The carb mixes the gas with the air so it will combust - straight gas in the cylinders won't burn as far as I know.
Make sure you start with the basics - you have spark. Do you have gas at the carb? My 58 has a bad fuel pump. It too sat for 15 years - The new pump should arrive this week.
You may well have gunk in the lines as well. Gas that sits that long will turn into varnish & sticky up everything it was touching 15 years ago.
Before messing with the timing check the fuel.
