Just got my first slant six

Might want to check in here and/or on slantsix.org and ask questions before jumping ahead and doing stuff that seems like it might be a good idea. Engine "flush" additives such as you put in the crankcase are a great way to finish off (kill) an engine—and you've worsened your odds on that by using a small oil filter instead of a big one. If you have an engine that's very dirty inside and you won't take it apart to clean it properly, do this instead.