What methods get used for cutting the top rails to width? I thought about using the router with carbide cutters but it's a Yugo and I'll have to modify a fence for it to ride along. Besides that I'm wondering if a hacksaw is a good chice. Probably alot straighter than I can get with my angle grinder or rotozip.

Angle grinder if you are skilled, cutoff wheel and dremmel works well too.

Cut them long and trim to perfection AFTER you rivet. then you can get exactly the amount of play you want. Watch the burrs that form on the underside, don't confuse the burr for needing to cut more.

The Global Trades receivers come a little tight, so you rivet them up, then sand down the rail until your carrier rides exactly like you want it to, not too much slop, not too little. And if you are really particular, leave a tiny bit tight, then shoot it dry for break in, then polish the edges. Holy crap...it'll even make the AR guys green with envy!

Yes, the angle grinder is quick, but be careful not to take too much off, and keep away from those lower rails. I use just the bolt carrier to test fit so often, when it's close, I use a 120 grit flapper disk on the angle grinder to finish up and polish the upper rails.