can the crossover tubes i see on alot of high perf engines be used on stock 1991 454 mags to replace bad water circulators . and maybe free up some hp thanks any install info would also be appreciated...

anyone

Yes, but don't think they are just a bolt on and go. Usually will have different temps and pressures than before. Sometimes you get lucky, other times........

ohhh thanks .. i will have to look into this a little deeper...

George, not that easy or cheap. must also change thermostat housing and rearrange some plumbing on the rest of the engine.
by the time you buy the parts for twins,you could buy a stock pump and be done with it.A lot of dicount place sell pumps or about $100. No pump , is worth a few more HP but with the pump you have a more uniform temp throughout the engine, eliminating hot and cold spots. Keep in mind Merc does their homework and if it wasn't really necesary they wouldn't put it on there! Not to say you can't do without it. But like I said , it's there for a reason.
Just my humble opinion, Good Luck.

I would do more looking also. You will have trouble getting temperature up at idle if you do at all. This is not good on a EFI motor and will cause it to run rich ALL the time. I spent one summer dialling in cross over set up in and got it pretty well but never was really happy with it. Put stock set up back on. Now I can run it at idle and get 160' water temp! All depends on your set up. Big Blower motor I run with no thermostat at all but for a stock motor or mild modified the stock set up works pretty well. Just my .02 Take a look at some of the ads for custom motors and you will find many run recirculation pumps other than on the really big HP.