Ok, so we know the engine isn't original to the car, so that clears up a few things. (A replacement engine wouldn't have a VIN stamped on it. It would have a CE code. More info on these HERE
The Muncie "may" be original, but you'll have to check the VIN stamp on that to make sure.
In 68, the 4.10 axle was optionally available on the Z28 and the L48 for small blocks, as was the M20 transmission, so your car (if the VIN on the Muncie matches your VIN), was probably one of those. Also note that if the 10.5" 403 bell housing shown in your pictures is original, your car started life as a Z28. (The L48 used the 11" 621 bell housing.) HOWEVER, the Z28 required power front disc brakes, which it doesn't appear your car has, so that rules the Z28 out. There are a lot of conflicting things on the car, so you'll have to do more research. I would say that IF the VIN on the Muncie matches your car's VIN, then it started life as as L48 (SS 350). If it doesn't match, but the car still has a 12437 V8 VIN, then it started life as either an LF7 (327/210) or an L30/M20 and none of the drive train is original to the car.
I can't tell by the picture of your firewall, but look at THIS PICTURE
and tell me where your speedometer hole is. The "Muncie Hole" or the "Non-Muncie Hole"?
By the way, what's your VIN?