Not sure what chassis,but on the b13 a popular mod is to retrofit B14 seatbelts in to get them out of the door.
It removes alot of weight from the door and you dont feel like you are getting strangled getting in or your gonna get ejected if the door opens...lol
I did my b13 many years ago at the time I replaced the hinges .
Its one of the best mods I have done to the B13
I actually have a set of b14 seatbelts up for sale right now from a partout if you are interested