How is the boat setup? Most Stevens' that I've seen are family ski boats. Don't recall much if any used in drag or circle racing. I doubt that it can SAFELY handle much more than it has without strut relocation and changing of propshaft angle.
Having (still own) a 1968 Stevens Flatbottom. I know mine was built in 1968 as a offshore marathon boat!! Hull & basic entire boat is 1 & 1/8 " thick thruout!! This boat when i bought it had a 427 chev with Crower Imperial roller cam installed & 2 = 4 bbl holleys. Casale vdrive. ran back the over 108 mph on rivers clocked with radar then. These boats were solid built & i cant say i have ever seen one go bad / deconstruct!! This boat i have has 153 hand formed alunimum pieces in it -with stringer caps running the entire lenght. all motor mount plates & all other pieces were hand made & cut. I had most of these anodized when rebuilding the boat 35 years back. Ill be selling all this spring as im getting old & just cant use it now.:yikes