I was in the same boat as you with my 1970 C10. I really liked the old 307 but when time came to replace it I ended up going with an L31-R GM crate engine. It's a vortec engine and I doubt you will find a two barrel intake for it but for the money it is hard to beat. For around $2000 you get a brand new 350 engine with 9.4 to 1 compression, 4 bolt mains, hydraulic roller can, vortec heads, and heavy duty valves. It even comes with timing chain and cover, balancer,oil pan, and valve covers installed.
You will need a vortec intake and electric fuel pump. The fuel pump nearly stopped me from buying one but most all cars on the road today have an electric fuel pump.
I wanted to keep the original look also but this is pretty close being the last version of the original 350 motor and with a lot more HP than the old 307.
I like mine, it runs smooth and has a lot of torque but not over powered. It really makes my old truck fun to drive.
I know this isn't what you were looking for but at least it gives you another option.
Here's mine it doesn't exactly look factory but I think it does have the old school look.
