If its an "R" block ie no numbers after the R then it will use a cam with 48 degree lobe spacings with std LA sized stepped journals. Cams blanks are hard to find and best bet with a new block is to have cam tunnel opened up to suit 50mm. If its cheap and is tall deck 4 bolt with 340 main it will be no different really when done than a new R3. I have one.
