Well I have both sets of heads off on my 500efi,s, machine shop found only 1 broken inner spring with no damage done, I am having them make a surface cut, machine valves and seats and replace springs, my question is i have almost 200 hours on the motors when should I change the stock chain and gear set??

Now would be the time, you have motor out. You can check for stretch in chain, but why not now, motor is out and its not much $$$. Do yourself a favor and degree your cam in.
Bawana

the blocks are still in the boat, I pulled the heads for the valve job and was just going to reinstall them soon but was wondering about the chains, i know they are a single row chain on the gen6

I would go with the Stock GM/ Mercruiser gear and chain set. No bother to degree the cam in on a stock 500EFI, no realized gains to be had. The stock set comes with the cam plate and new bolts as well. I have a GM part number of 12371053 for a Gen VI 502.
Dave

there is not a big selection for the gen 6, i have a A Frame i can use to pull blocks out, was just wondering what everyone else was using for a chain and how much slack was in one with close to 200 hours

At 200 hours, you'll probably have quite a bit of slack. Of course, if you had 20 hours you would have quite a bit of slack. The single rollers stretch quickly and then level out. I would recommend changing it to a double roller. Rollmaster has a true double roller with billet gears and a 9 keyway crank gear. It takes just a little clearancing of the cover while you have it off. There are some reinforcing ribs in the top half of the cover that have to be ground out. Not a big deal to do. The timing sets run a little over 100 bucks. The only other that I know of is Cloyes single roller. It is a 1/2" pitch chain, but still a single roller and is like $160. Give me a shout if you are interested in a couple sets. Hope this helps, Eddie.

the rollmaster sounds like the ticket!! I will give you a call ASAP. thanks
Mark R

Rollmaster with the IWIS chain is what I would recommend also. Very good timing sets.