As for your 4x36 Al, I have a link to James McClendon's YouTube channel and take a look at how he modified his grinder. He cut notches into the sides so he could do a plunge line. And see how he modified it to do a hollow grind. James is known here at TKN as jmcustomknives, I think that's it. He forges a lot of crane cable Damascus and also does file knives. James says in one of his videos that he's been using a 4x36 so long he doesn't think he could get used to a 2x72. I modified my 2x48 by screwing an 1/8th inch by 2 inch wide by 8 inch piece of stainless onto the 2 1/2 platen so I can do plunge lines. I could do a modification like James has done for hollow grinding, but I am very fond of flat grinds too.
Here's how he modified it to do a hollow grind.
https://www.youtube.com/watch?v=eRqhays5vEc&t=3s
Here is his home page for YouTube. He has a nice video on testing a knife as well.
https://www.youtube.com/channel/UCth...Q8uuvpB2PJXSkw