I remember reading something about these Irons in particular. I searched for it but none of the threads had anything really to say. What is so special about these irons?

 

Big stock ports.

 

Wrongo! They are the same as any '76-'85 stock 12A, but weigh a little more than Y plates. There are a few different variations of R5 plates; some had small GSL-SE sized primary ports. Most others had the same tall runners and 12A-spec port timing as any '76+ 12A or '76-'78 US-spec 13B. They come in nitrided and non nitrided. You can port them as large as a Y plate.

 

Are those the ones that...Jeff20B I think, is such a fan of?

EDIT Appears as he has posted at the same times as me...

 

Ah, because I just found out that my Half street/bridge plates are R5