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You guys race these motors. It looks like the 60 hp 59 cubic inch motor is a different block to the 40 hp.
Can a 40 hp block be easily made into a 60 hp.?

Will the old 3 cylinder 90 hp mercury out of their jet boat mount on a 59 cubic inch outboard tower?
I recall Fred running one in the 1990's, but it was only rumoured to be one.

Paul and I were discussing that very subject earlier this year.
He indicated he'd performed upgrades to 59ers in the past and was thinking about taking it to the next level. Don't know if he did go there but it may be worth a phone call

Correction...that would have happened in 1996. The 59 cubic inch motor did not appear until 1998 so the tower is the 52 cubic inch 60 hp. The 52 is a much weaker motor. If you look up the 1996 Dunnville race on YouTube it is easy to see that Tammy is not running a 52 cubic inch powerhead. She is the fastest off the dock and it is the inexperience in driving that holds her back.

the 59ci 60hp run different port timing . you will need to fit 60hp sleeves and match the ports , remove the reed stops and run the washer style stop + find your self a set of 60hp carbs.

That is what I found out as well. The motor was sunk and the owner did not know that all they had to do was get the water out of it to save it. It is rusty and only good for some parts. Good news is it is a low hour short shaft. Currently doing tear down to see what is good. Next will be a visit to Top Gun to see what Paul has 60 hp.

Speaking of 40hp mercs, how does the 1989ish 4cyl merc compare? Could a good 44xs powerhead be competitive running in T750? Not that I am getting another T boat, but ya never know I like the idea of something different giving those 2 cyl OMC's a run.

Since the 44XS in race form runs in D class against the 50 Tohatsu, I would think that it would be competitive with the Tohatsu. To date we have never raced a fresh, blueprinted Tohatsu in T750. All of the T750 OMCs are right up to race specs. I think the best we could hope for out of the 44 Mercury and Tohatsu is 60 hp. The top OMCs appear to be in the 65 to 67 hp range. Weight is the key. A good Tohatsu or Mercury weighing in at 500 lbs will give a good race against an OMC weighing in at 700 lbs. The problem is. put a race prep OMC on a 500 lb outfit and it will easily beat the Tohatsu or Mercury. Plus the OMC is far less money to buy and to race prep.

why is there no 2 cyl OMC competing in D class

They are not a legal motor for the class.
DSH..... Tohatsu TLDI-50 on 44XS or Scottcraft mid with Komato gearcase (Probationary)
Mercury 500 series motors 1976-1989

The 2 cylinder OMC was banned from DSH many years ago (80's?)... too fast on a hydro in race trim. That's when they created the 45SS class (and 45SST). I saw one go once at the US Nationals when it was probationary engine... it was a rocket. Waited at the end of every straight. Would have likely lapped the field if he went for it. Didn't suit the class.