the assembly manual should show you how the small block was installed and what linkage looks like etc.
https://www.trifive.com/d1/55-59Assy.pdf
you will need a new bellhousing, flywheel, clutch etc to fit the small block but the bellhousing will sit on the cross member like the old one and likely could use the same mounts there if the old rubber is still good. find a 55-59 v8 truck or 55-57 car bellhousing.
you will need a starter that bolts to the bellhousing from same era v8 and then you will need to install a starter button to replace the "step on the starter" pedal, if thats what you had before
depending on what year of engine you buy, you may need to drill and thread the front motor mount holes in the block. some had them and some didn't
the front engine mount may interfere with the fuel pump spigot but if you get the right pump the spigot can be indexed to a different angle so it fits fine. if you have power steering the motor mounts may interfere with the pump mount
you will need some ram horn exhaust manifolds and then some simple exhaust hookups
if you decide to go with a more modern rear transmission mount instead of the crossmember behind the engine, but want to use the stock front mount engine mounts then think about bracing the engine somehow with a torque limiting device (chain usually) so the engine torque doesn't allow the engine to twist up and bind linkages etc.
if you do a search on this site you will likely find a thread on the small block swap and what parts you need
engine mounts
https://www.classicindustries.com/pr...ts/556038.html
trans mount rubbers
https://www.classicindustries.com/pr...rts/14501.html
exhaust manifolds
https://www.classicindustries.com/pr.../a7700104.html