They are probably mirage or mirage plus props. I am guessing Mirage as that is what most Formulas of that time frame run. Mirage plus's are ussually labeled as such, so my lean is that you probably have Mercury Mirage.

The 23p Mirage props were from quicksilver if I am not mistaken.

I have a 89 311 bravo's and until 2010 running 365's Mags with stock 23p Mirage. I have seen speeds between 64-65mph and even on a good day she was not faster. Both mag's were spinning 5200rpm at that speed.

In 2011 the boat was repowerd to HP500's with 26p bravo's. Even now it has to be a very good day to get 72mph.

The speeds you are seeing with that load against the current amazes me.

Weird. Guy I bought it from said always between 66-68 on GPS. I didn't think that the speeds were anything great. I had a smaller boat but was faster then this one. I was more looking for a comfortable ride. I did drill holes in swim platform so I'm not sure if that makes a difference also. Maybe my GPS is off. The one thing I will boast about is how theses boats handle rough water. I was amazed how well it did in 4 footers.

another thing i read which doesnt mean much is that every extra 100 hp is roughly 3-5mph...so if my boat has 70 more hp then you that sorta makes sense