It's a tricky one. You're twice my age and have more side hair than me lol. Have you tried concealers on this area? and testing out how well they work in the rain and when you sweat?

The two I recommend are:
1) Dermmatch, mix with freeze hold hairspray not water as they recommend.
2) Toppik, then spray hairspray ontop to keep it locked in.

A possible thing to think about is tattooing the sides, but this would mean you could never shave your head for a bald look.

How well does this template match up with your previous topper template for the front?

Younger guys get carried away and try to have a too low hairline, having recession helps it look natural. What hairstyle would you be going for?

Also how long would you do your reattachments?