First, don't expect the V8 conversion motor mounts for an S-10 to put the engine in the right spot for your truck, because the S-10 cabs (and therefore firewall) are located much differently than your 53 cab will be. When we do these swaps it's always easier to get the engine mounted first and then mount the cab, but to each their own.
You may find that the engine is in the right location with the 4.3 mounts on the engine, or you may need to move it back a bit. The conversion mounts for an S-10 won't put it in the right spot though.
Take lots of measurements. You may need to make your own mounts to move the motor back with some flat plate or something similar.
My dad's 52 has a 454 and uses the stock 4.3 mounts (same as SBC and BBC) in the factory S-10 location. His firewall is uncut. However, yours may be different based on where your cab is located.
The biggest changes to install the 327 are figuring out where it's mounted, fabbing the transmission crossmember, and getting the driveshaft figured out.
