The front engine mounts for a '58 235 are side mounts. On the cars, the mounts fit the triangular hole pattern about midway down the block. On the trucks, they fit in the very front, so far front that they are under the generator bracket on the driver's side. The blocks of the '58 235's were made to accept either type of mount.
I'm beyond my expertise on this next subject, but here goes...I'm pretty sure that your '47 Fleetline has a front motor mount that uses the base of the timing plate to connect it to the front cross member. It would have two square holes for 7/16" fine thread carriage bolts that bolt from the top down. The '58 timing plate does not have those holes...unless you got real lucky and GM had so many left over that they were using them up!
Someone else will know if the timing plate on the 216 is compatible with the 235. It may be. If so, you can switch out timing plates so that you have the correct holes. Not real easy, but not real hard. Might require going deeper into the engine than you care to. If you go this route, be sure to install the carriage bolts early in this process because one of them can't be installed later on.
An easier solution? The timing plate on your 235 can be adapted without removing it. You have to be very precise when you do it, but it can be done. I did it once for a friend who was installing a TF 235 into an AD truck and had the same issue. I made a template showing the locations of the holes, aligned everything very carefully with the center of the crank, then marked and punched the holes, then drilled them. I put a 7/16 fine thread bolt through the bottom of the hole (reverse of the carriage bolt direction), secured it with a nut, welded the nuts in place, then removed the bolts. Voila...weld-nuts in place to fit the stock motor mount. That allowed for the motor to be mounted with bolts from the bottom up instead of with a carriage bolt from the top down. I did this with the engine raised high enough on an engine crane for me to work under it WITH MEASURES TAKEN FOR SAFETY. I removed the harmonic balancer to get room, but nothing else had to be taken off.
I will gladly stand corrected if I'm wrong. I have only done this when prepping a TF 235 for an AD truck and have no experience on '47 cars.
Matt
PS--This Tech Tip explains the timing plate swap better than I did!
http://www.stovebolt.com/techtips/engine_swap_216.htm