Car stereo replacement elastic drive belt

[Stevo302]

Hi, does anyone here know about old car stereos?
I have a Philips car cassette player N2 602/00 and i need a replicant elastic band. I've tried to google a few things but how do you measure the length so i can order a new drive belt? I've put a wire round there and is that it? I need 305mm long one?

Also, where were the original speakers fitted in the Vixens?

Thanks.