you could look for a nice used 235 to drop in. they are available here at the swap section, on eBay, and Craigslist. depending on condition they are generally way less than $1K.
Searching "chevy 235 engine" on eBay brings up a running motor in a Bel Air for $750.
ask to do a compression check on any engine before you buy. paint up the motor and swap it out - no more work than removing/reinstalling your existing motor. you might even get a little back for your worn motor as a rebuildable core ($100-$200).
since you have a '57 engine in your '54 truck, you aren't concerned with a numbers-matching situation - all the more reason to just go with a used motor swap.
my $0.02. good luck!
