The larger block is reversible, and changes the gap between the two blocks. It's probably missing a roll pin in one hole. They are not magnetic. It can't be real old because of the vinyl grip. Only markings are "Made In U.S.A." and "Pat. Pend.".
(https://i.postimg.cc/G37Sdv9T/IMG-9680.jpg) (https://postimg.cc/rz49901q)
(https://i.postimg.cc/FskGvq2w/IMG-9681.jpg) (https://postimg.cc/BXs2chZC)
(https://i.postimg.cc/fRXHcFCY/IMG-9682.jpg) (https://postimg.cc/21kFm0P5)
(https://i.postimg.cc/9Fs8qVdW/IMG-9683.jpg) (https://postimg.cc/ykXXwMp5)
(https://i.postimg.cc/59RpZ1kw/IMG-9684.jpg) (https://postimg.cc/kDWxSrC4)