Or, conversely, is your 1948-technology Fox 35 enough, or should you change to a 1990-technology 25LA which more than makes up for 40% less displacement with a higher RPM and generally more efficient operation?
For comparison, a 20FP (20, not 25) is more than enough engine for a 32-ounce Ringmaster. I'm not sure how big a Dolphin is, but I suspect that engine would work in it.
Note that OS confused things by making two versions of the 25LA -- the original production run is wimpy compared to later engines. No one's figured out why, but if your 25LA won't pull a 33 ounce aircraft with authority, getting another one may solve your problem better than a Fox 35.