Plastic tank , will it fit?

I have been offered a plastic Fuel tank from Kendal , I was wondering if the later plastc one will fit straight in?

Some guy on ebay was selling a plastic one but said it didnt fit his earlier rangie even though he was told it would.

Am I safe getting any plastic tank? will any metal/plastic tank fit my classic 1990 rangie?

I need to let him know ASAP

Thanks

John