Hi
I have been building FE motor's since about 62 or 63 for street and race. In the early 70's [72 or 73] we started installing hardened valve seat's in all of our build's so even if you have a c1 or c8 head etc. you could allready have the hardened seat's in it if it was buildt after the early 70's.
Even if you don't have the hardened seat's I have found out that you won't have any valve damage untill after 40,000 miles on the engine. I have pulled down engins that never had the hardened seat's with 55,000 miles and they had very little valve wear or seat wear but were ready for the hardened seat's.
As to the additive's I have never used them and don't recommend them for a well buildt motor. If you are worried about lube then if you add a small can of 2 cycle
oil to each fill up you will be fine.
Greg