Hi Baba,
BTW, what is wrong with your valve covers? Are they leaking? Depending upon how bad they are off, if the screws have been over-tightened over the years and bent them, or if the prop-side is leaking from not being true, a lot of times they can be carefully straightened. S&W's mechanic, Chris, ended up doing this for my old boat.
I think he said he had metal stiffeners that sit atop the cover in the grooves where they are screwed down that he could use to help stop leaks, too.
The valve cover leak I had on my old boat's port engine was easily the most frustrating repair I've ever had. It must have taken half a dozen attempts to get it to quit oozing.
Their next move was going to be replacing the valve cover. And, they had prepared it to install (blasted, painted). But, they didn't need to do it. I had called them about it in May and plan to buy it next time I place an order, just to have.
But, if someone who needs it gets it before my storage locker -- the world is better off.
(Yes, I am crazy about such things as valve covers oozing).