If you don't have a milling machine or lathe to cut it perfectly square, you can buy fan spacers of various thicknesses on ebay. I had to try several to get my fan perfect on my slant six (very tight). Looks like you have plenty of room to move your fan back on your big-block. I also used that aluminum water pump housing on my 383. It must vary slightly from the factory cast-iron housing since I had to fuss with pulley alignments a bit. If you use an aftermarket damper, that can trigger such changes too.
