Have already emailed them. They have no idea why it won't fit and what can be done. They referred me here. Some have done it. They have montes on zzp site under member cars running their oversized rad. I found a place in Cleveland oh that has taken a veh apart with the zzp oversized rad and told me why it won't fit and what it looks like their customer did to make it fit. Someone on here has to have more info . I'm in the same position. Cracked rad and looking for something better than just oem

 

when looking at the specs for the 98-99 models it looks like they two different options for the radiator w/o hd cooling and with. Looking at my car i think i see two radiators i wonder if thats the hd option? they both look to be 5/8 in size.

 

Can get underneath or above to get a measurement.. ive been told its either 5/8 or 1". i have a 99 monte z34 3800,,if anyone can help please fill me in