There isn't anything wrong with a PROPERLY INSTALLED block guard. You need more than a hone after install also, a bore is pretty much mandatory to ensure consistant diameter and roundness.. Weld-in block guards are the way to go if you're going that route, else just shitcan the idea of a blockguard and get some sleeves. I'd still sleeve it if you can afford it, there is the least amount of comprimises and best performance.

Coolant temp rise depends a lot on the block guard and the block/head jacket design. Some block guards work ok for cooling, some don't. Most still tend to limit cooling flow right at the head interface and make some local hotspots.

Pinning is ghetto and doesn't do anything except keep the cylinders from moving around a little. The block will still deflect and let the cylinders move, the support just isn't there.

Whether you need it or not for what you're looking to do is debatable though.