Slant six head

on positive seals, there are many that will fit, even though not "listed for that application". I had bought mine via Ebay, think I paid ~$10 for a set, that was said in the listing heading as being "for" a slant 6. I had taken in both styles (positive and stock style umbrella) and said to use whichever ones they felt more appropriate, and I can see that they put in the positive style seals.
That said I know they have a drawer full of random ones, I did some work on a twin cyl Kohler and took my old ones in, (what was left of them) and they "matched some up" for me, handed them to me and said "have a nice day". Kohler wanted something stupid like $18 each and there are 4 of them on that particular engine. Your machine shop of choice probably has plenty on hand, as well.