Will the SiR bumper lips fit on the OEM bumpers on my standard model HB? Or can I buy the Si bumpers and put them on those bumpers?

 

Don't quote me on this but I think it wont fit, because you need the "pre-lip" the SI bumpers have.

 

If i remember correctly, there were three different styles of front oem lip options. The SiR is made for the longer front end which is a different. In North America, there was both an option for 88-89 and 90-91 style which differed slightely

 

^right on point.