You did not say if you want to take the automatic transmission along in the swap.
If you do bring the a/t AND you have the entire donor car sitting next to the receiving car, you will be able to accomplish this with much work and care. It may take such items from the donor car as the driveshaft, exhaust system and who knows what.
If your goal is to retain the manual transmission, you will have your work cut out for you. To begin with the crankshaft as it relates to the pilot bearing is different from auto to manual. The bell housing of the transmission would mate but would put the engine too far forward. Moving it back would require a different length driveshaft, it could be that the 300D driveshaft would work. It would also take different length shift rods and possibly clutch lines and speedo cable.
The success of this swap, either way you go, will be determined by your level of determination.
BTW, There is very little difference in engine weight. If there is a spring difference, you could take the springs from the donor car, but if you left the suspension as is there would be no weakness, just slightly incorrect spring rates. These suspensions are the same throughout the 123 series.