If the Weaver cars are scale length, the LIONEL you i.d. won't be a good look since it's only ~4.5" in length for use on the 15" aluminum cars; typical domes for scale length cars are 6" to 6.5"--I've been investigating the dome lengths for a project.
LIONEL also sells a dome used for their 21" scale length cars which you should consider--IIRC, it's 6.5" in length. You can find the p/n on their website.
Good luck.