Quite late to this one but have some info. If you plan to drop a V8 in a 86-89 its do-able. The 89 Shelby Dak had a LA 5.2 with TBI. The fan was elec and had to be a pusher do to room. If your doing a 90-96 its much more do-able because they came with V8 from Ma Mopar. You biggest problem will be the oil pan and pickup because the Dak has a very large X member that requires a very small sump area all the way at the rear. The Shelby and 90-91 pan used to be available but Ive exhausted every source and they all say disco and gone.
Im about to put a 340 in an 87, an 86/7 is the best model IMO because it was carbureted from the factory so emissions and race tuning is easier. Im using the stock 340 pan rail and welding on a rear sump Magnum 5.2 pan lower section.
Modifications will vary dependent on what year and if SMPI, TBI, carb and then what type of engine, LA, Magnum, that you use. LA to a SMPI is the toughest to do due to accessories, CPS, etc. You want a great base, start with a 94/5 Dak 5.2. It has OBD1 and is very forgiving with mild mods. 92/3 had the most stock HP but doesnt have an airbag but does have return style fuel system so it lends itself to tuning very well also. Feel free to PM me as I have been working on Dak's since they were new, just about.