It maybe wasn't a consideration then, but now the later engine with long water pump and late accessories would come in handy. As others pointed out you have more options with a later block & accessories, namely a PS pump location that's higher and closer to the crank. It gives more clearance from the frame and saginaw steering shaft.
Perhaps don't worry about the 1" offset for now. Mount it centered or whatever is needed for clearance and let the driveline be slightly off side to side. It's not going to wear anything out especially for the amount you're likely to drive it. Then watch for a late 5.7L to swap in and when you do, then move it to drivers side the 1" needed to line everything up. With AA engine mounts it's as easy as sliding it over a bolt hole.
Perhaps don't worry about the 1" offset for now. Mount it centered or whatever is needed for clearance and let the driveline be slightly off side to side. It's not going to wear anything out especially for the amount you're likely to drive it. Then watch for a late 5.7L to swap in and when you do, then move it to drivers side the 1" needed to line everything up. With AA engine mounts it's as easy as sliding it over a bolt hole.