The ASP 52 will be great for that plane - I've used the same combination. Far from being a "Hunk of Junk" I think the ASP 52 is a powerful and easy to handle engine - I have two of them. It will pull the Harrier up out of sight very quickly with that prop. I used a 13 x 4, which also worked well.

The four stroke will be a bit too much and is unnecessary weight. I have flown that plane with the ASP 61 four stroke (okay, but a bit slow out of the vertical) and a JEN 56 (not as good as the ASP and a b1tch to tune).

Stick with the 52 - it's a good match for the plane.