[Bill Eveland]

Hi 55 Chieftain, welcome to the group.
The last 55 I saw with a Chevy smallblock had a front mount installed. It's used a front plate mount similar to what Speedway Motors sells, they have a website that shows their mounts and accesories.
They used rubber isolators from the front plate attatched to a welded fixture on the front crossmember. Again , Speedway Motors should have what you need to mount the front of the engine.
You'll have to make a rear mount for the trans, either th-350 or 400 as long as their short tail shaft to clear the x-frame.
You will need to make a middle support also, you don't want to have just a front plate and trans mount or you have a good chance of breaking the tailshaft. Try to tie into the original trans crossmember to some of the transbolt holes.
A driveshaft,trans linkage will need done, something else as far as the exhaust goes, you may need to use passenger side manifolds on both sides to clear the gearbox and master cylinder on the drivers side, If the 287 is still in it , you can see how the exhaust needs to be routed on the driverside. Dual exhaust is tricky especially around the under seat floor heater.