I found a few 302/351 adapter plate manufacturers or sellers:
http://www.pricemotorsport.com/html/body_intake_adapters.html
http://www.flatlanderracing.com/pmespacers-01.html
I suspect this one is what youre looking for:
http://www.pricemotorsport.com/html/body_ap-01___ap-04___intake_adapter.html
If youre going for high hp maybe you should look at an aftermarket 351 intake from summit or somewhere. Im sure it would do ok with the 302 intake because of the turbos, just that the same boost would be a bit less efficient.