Trying to identify gearbox

[Slugger1990]

Hi all. I currently have an e36 compact fitted with the 328 engine but I'm unsure what gearbox is fitted to it. It's a very short ratio box. The guy I got it off said it was a 1.6 gearbox but Iv been in a 316i at higher speeds than mine will go to without limiting. Could it be a custom built box ? Or could it be getting limited from the ecu ? Any help welcome