That’s a tough one since IIRC if you’re not using ember-cli it’s anyone’s guess exactly how things are wired up to build, etc. At a high level I’d think you’d want to try adding ember cli at roughly the same version (2.14ish), ripping out any build related code from your project and focusing on getting it to build correctly. I imagine you’ll have some 3rd party libraries that you may need to work into your build differently… Does it use broccoli for building still?
Once you’ve got ember-cli working you could step through the upgrade process from there and it should be much more straightforward.
Unfortunately I only barely remember life before ember-cli, but maybe someone like @ef4 would have better tips.
here are a few resources that may be helpful, depending on what you’re migrating from:
Also you may need to drop your node version way down w/ nvm before attempting this. Maybe try node 8ish?