I’m thinking of putting together a lightweight scout style rifle. Caliber will be either .223/5.56 or 7.62 x 39. My thought was to get a Ruger American Compact or an American Ranch Rifle. The challenge will be getting a forward mount and what kind of scope?

Any ideas or suggestions?

Ruger would be a good choice. You can always have the barrel tapped to mount a short 1913 rail.
I would suggest a Burris 2-7x scout scope. Really nice glass & gives you a decent range of power settings.
I have two Ruger GSR's (one in 308 & one in 6.5CM) not the calibers your looking for but they are outstanding rifles.
FWIW, Ruger does make a scout rifle in 5.56.

Take a look at the Mossberg MVP Patrol Rifle. Chambered in 223. Mossberg makes the same gun in full on scout form. The only real difference I could see between the two is the scout has the full length forward scope mount rail and is chambered in 308. My guess is the 223 could also accept the scout rail without a lot of fuss.

I've shot the Mossberg MVP mentioned above. It's a nice rifle. Easily made 200 yard shots with a properly zeroed 3-9 scope. The only complaint I had was that the Fiber Optic front sight wasn't as robust as I would like, I believe they have improved it on later models.

I've got the .308 Ruger GSR and with the wood stock and steel magazines and it felt a lot heavier then the Mossberg to me, which is interesting because on paper they are within a couple ounces. Great quality rifle and can be switched to a synthetic stock.