Sorry we had to talk on such bad news. I ran some numbers on the seat duration to see what overlap numbers looked liked as we did take in account on this build that you wanted a sound build that could use the short risers.
Mercury Mag 502 engine with cast iron manifolds has 57 degrees of overlap
HP500 Carb Engine and the shorts has 68 degrees of overlap
28Eliminators cam has 59.5 degrees
I called a ex Crane guy that was at Crane during the 90's and asked him about 60 degrees overlap and injesting water. He said 60 is no issue.