The engine lasted this long no need for it to explode now. depending on whether or not the engines been changed you may get too 105 hp. Some of the trucks had mechanical governors to keep them at 45mph or so but these can be removed just remember the braking systems are not up too todays standards. If you make the changes diesel etc the next owner would proably buy it because of the work you've done rather than because they want to change it back. Build it the way You like it.