"looking into ive decided against the flat head, and going for a 350"
Now you're making some sense. The 283 may be worth more for it's parts than as a complete assembly. If it has ram's horn exhaust manifolds and Chevrolet scrip valve covers, you could ebay those off for about as much as you'd get for the engine as a package. Maybe the heads might be worth something as well if they are desirable.
As far as your transmission is concerned, if it fits the 283 now, it will fit the 350.
Personally, I'd squirrel the 283 away in a corner, and when funds allowed, I'd have it rebuilt or at least looked at by a pro. Maybe it doesn't need a complete rebuild. You may aquire another project in the future which could use the 283. Nice little engines to have around.
