I'm probably getting in on this one a little late, but...
Since you have the engine block in already, take the Xacto knife and make a 1/8" cut (sideways) in front of the engine block between the fins (Not where launch lug is).
Get an engine hook and a Mylar retaining ring (both available at eRockets.biz).
A link for your convenience.
RING
HOOK
Insert the engine hook. Since it's built, you'll have to cut the Mylar ring.
Glue it over engine hook with the cut on the opposite side of the engine hook.
A few of Estes' older rockets had this form of engine retention when they first came out.
Before engine mounts became common.
It might help if you cut the Mylar ring at an angle opposite the spiral wrap. It would be harder to pull away than a straight cut. If you can fit 2 that would even be better, cutting in opposite directions.
Cutting against the spiral wrap won't weaken the wrap as much and retain more of it original shape.
You can even paint it if you'd like since the color is milky on the Mylar ring.
I personally like the Viking. 3,4 or 5 fin design with several mounting surfaces to choose from.
I have even used 3/32" balsa on the last one I built due to the card stock layers on the fins can separate on hard landings. I like the high viability of the new paint, but prefer the old style decals. Much more appropriate. And the Viking is a high altitude flyer on a budget...if your eyes are still good enough to see it.