Correct, the R7 is a casting number not a grind. I have 3 early engines in the shop, I put the best parts on a sandcast motor, I was hoping to find a low R number but it's not a huge deal. I'm not sure that an R6 or R7 wouldn't be correct. And it's inside anyway.
I'm using the best parts of the other 2 for a diecast engine for either a 10,000 era serial number bike I don't own yet or my 14,100 bike.