Depending on which (318-360) you decide to use you may have to use a truck pan and pick-up as Feets hinted to. Dimensionally check the design of the existing pan and compare them.
As for the motor mounts, driveshaft and exhaust since you can fab you should be able to make something there work.
I'd say if its an older model without a lot of electronics it shouldn't be a big deal...
SBC's are everywhere for not a lot of money...I'm not sure a swap is the most fiscal approach...