Probably best just unscrewing and having a look, mate. Even if you match the correct size.. you've got to still get the correct depth and positioning on the screwholes of your new speakers.
That said, Autoleads, among other companies, make speaker-adaptor kits. Search for them on places like caraudiosecurity.com etc. and see if they can supply an adaptor kit for your 1.4s. Not only will it tell you the correct diamater of the speakers, but it'll also show you what options are available.