E36 vert project

Well after long hours getting a business up and running I seam to be getting somewhere that I've gone and bought another e36 vert in se disguise now it's no looker or goer for that matter but that is all going to change ,,body work is in what seams to be great condition and the fully electric roof works but it does need to be re stiched in one part as the treads have frayed and exposed one of the spars the interior is cloth but that has been sorted with a new(2ND hand) champagne electric heated sport interior including all door cards and plastics ,wheels are as good as sorted (BBS rc041/042) but with a difference I'm going to use the 042 on the front and have the fronts widened for the back now this is where I need help ?the bumpers are se which are fine but I want sport and are nearly impossible to find good ones (plastic not fiberglass)and the engine is 8valve which wouldn't pull you out of bed,,so out with that and in with the new either 325 or 328 what I need help with is,,,is it a straight forward unbolt my box and bolt to the new engine or do I need everything from engine to box to running gear and does anyone have one at a reasonable price,the whole car is getting stripped to be painted and polished anyway so I don't mind if I have to replace the running gear just not 100%on what I need all help greatly appreciated