Those rubber grommets allow the Rad to move when the chassis is flexed..The reason is that if you Bolt down your rad Securely with bolts and NO ability to flex then the rad and it's core/fins will have to absorb the Chassis's flexing.
This would in turn make the rad more subseptible to cracking or leaking.

 

Herpaderp.. here I am thinking only about electrolysis lol

 

reviving an old thread because I make vm kits and I have the answers you need.

https://www.rx7club.com/group-buy-ce.../#post12055026

 

I would like to update as some time has passed...

I went with the HH series radiator which fit very well and has been doing wonderfully. Coolant temps are very well controlled even in the Georgia summer heat and having some fun with the car.

Setup in a nutshell is streetported high compression 4 port with a hybrid turbo, full exhaust, etc.

I run a stock fan in medium condition and the factory shroud and NA fan blades.

The only out of the ordinary thing I did was take window A/C sealing foam (charcoal in color, comes in a roll, no adhesive, about 2 inches thick) and sealed up the gaps around the radiator.

I have no complaints about the HH series, and would definitely recommend it to others.