Check for balance on your 727
make it the same as the 518
also use the 727 converter or change the 727 to lock up and you can use the 518 converter
there are several 727 converters
get one that matches your cam, gears, usage, towing etc
a high stall converter with tall street gears will get hotter
perhaps start with a club cab long bed
or a full size pick up shaft
find out how much shorter your 727 is
then crawl under some vehicles in the local pick and pull with a tape mesure
at the end of the day you will most likely have to have a shaft cut or a new longer tube put on yours
If you replace U-Joints use only genuine Dana-Spicer
i doubt that any factory shafts will be the right size. Measure the space you need for the drive shaft and if its shorter than the current shaft (or the shaft you pull from another truck) you can easily shorten it if you are a welder, or you can get someone to shorten it for you.
What year truck is it? The truck will throw codes for OD lock up probably. The swap itself should be easy. The driveshaft is the hard part if you can get an exact measurement of what you need it's as simple as going into a shop that specializes in that.