I have some strong opinions on the SL8. Flame away.
I have an SL8-5 (black, long rail, vented fore).
I personally like the look of the rifle.
Accurate. Well built.
A bit on the heavy side.
I'm not crazy about so much plastic.
If you put a long bottom rail onto it and a MagPul AFG2 it handles much better.
Mine has the bottom rail, AFG2, short AR Riser to save the plastic top rail from ring clamp dents, Leupold Mark 3-9x40 T2 .223 BD, HK Sling.
I wouldn't do the mag well hack, it isn't worth it.
You'll hack up the SL8 and its value will drop significantly.
I would never buy one that has been hacked up for the mag well adapter.
If you don't want to pay for the HK original mags, just buy some of the Spear NZ SL8 magazines. Available in 5/10 or 5/30, clear or black fiber reinforced poly, ~$45 from Wolverine. And the Spear mags are better built than the crappy ASC LAR-15 mags that you would use with the mag well adapter (I stopped using ASC LAR-15 mags in my XCR-L and switched to only RA XCR branded ones because they are built so much better).
And if it is 5 vs 10 rounds you are worried about, does it
really take you that long to swap a mag?
Hacking an SL8 into a G36-wannabe is a waste. Especially for the high price.
And you
don't end up with a G36 (posers).
It's like saying "Look, I put some AR-15 parts onto my .22 and now I have an AR-15!".
If you want an SL8, get an SL8 and leave it as an SL8.
Most of the bastardized SL8G36 look terrible in my opinion and are a
huge waste of money.

If I was throwing that kind of money around I would just get something else/better.
Personally, I prefer my XCR-L over my SL8-5 by a large margin (much more fun to just throw lead down-range), but the scoped SL8 is good for shooting 100-300yd paper with decent accuracy.