150 to 450 convetion

i am trying to put a 1.5 ton suspetion on a 150 fram that had a ambulance package on it when i got the truck it had a regular bed on it now it is a flat bed it has a 300 inline 6 and 5 speed manuale trans it also has 4x4 and the front is twin ibeam ifsthe tuck is sound but i whant it to hold the weight with out saging if there is a easyer and less expensive way please let me know i also want to put a turbo on it if any one knows of a place i can get one it would be appreciated