Re: Play in steering wheel:
The Mercruiser 5.7 are power assisted. I believe there are different gear ratios on the rotary "no feed back" steering. If you like the one you're using, count how many turns from lock to lock. Then, see if they have the same for the Rotary gear.
Teleflex is the big company for steering gears. They have a good reputation for customer service if you have a question. The other company was Morse, which was bought out by Teleflex.
The trick is to get the right cable length. Most cables have a number on them. Or you can take out the old one and measure it. Examine the route the cable takes. You can use the old cable to pull the new one. Or draw a light rope (pull string) when you remove the old cable.
Sometimes you find the Rotary steering kit and cables for good prices on Ebay. Just be knowledgeable about the model, # of turns lock to lock.