I don't have any idea about the camshaft clearance, but the journal size is no issue. Back in the seventy's, Bill Jenkins, of Chevy pro stock fame used a little trick to run the prefered small journal cranks in the stronger large journal blocks, it follows...
Find the 250 block that you want to run.
Buy a set of .020 undersize bearings, take them out of the box and scrape all the babbit off of them and install them in the block and caps.
Drill an 1/8" hole thru the shell into the cap and block (on the oposite side from the oil hole of course) and install a roll pin.
Now you have a block, when the caps are installed that has a main cap bore of 2.378 plus the babbit thats missing. now go talk to your friendly engine machine shop and tell them you want the block line bored to 2.4016.
Now you have a 250 block that will accept a set of 200 bearings and therfore crankshaft.
If you read this procedure and think I'm off my rocker, it's detailed in Jenkins' book The Chevorlet Racing Engine, and it was good for 2 hp per ci in 1976..