Maybe use a straight edge aligned with top and bottom nut slots. Set the straight edge center of low E at the nut and align the edge with the edge of the neck where the low E string would go. Align the other end of the edge with the bridge saddle of the low E. Make a mark on the body with a pencil around that side of the bridge plate as a reference point. Do the same thing with the high E side and make a mark there. You might have to interpolate both sides of the exact position of the bridge if they don't line up perfectly with the neck but you'll get it pretty close. You can still adjust the neck angle after the strings are on anyway. Also if the bridge is a trem make sure you give it enough forward space for the block to move up and down.
Guitars/Bass - MIM Fender Classic 50s Strat, MIM Fender Standard Strat, Squier Classic Vibe 50s Tele, Gibson Les Paul Studio, Epi '56 Gold Top Les Paul, Martin DSR acoustic, Sigma Martin Auditorium electric/acoustic, Squier Jazz Bass.
Amps/Cabinets/Modelers - Model 2558 50 watt Marshall Silver Anniversary Jubilee combo w/ Celestion Vintage 30s, 4x12 Marshall cabinet w/25 watt Greenback Celestions, Fender Blues Junior w/ a couple of Billm mods, Line 6 POD 2.0, Roland Micro Cube
Pedals/Effects - Cry Baby Classic Wah, Boss TU-2, Boss NS-2, Boss RC-2 Loop Station, Ross Compressor, MXR Micro Amp, Danelectro FAB Echo, Danelectro FAB Chorus, Danelectro Chicken Salad, Marshall Guv'nor Plus, Marshall Echohead, Duhvoodooman's Zonkin' Yellow Screamer, Digitech Digiverb, Digitech Bad Monkey, Dunlop Fuzz Face, Homemade Loop Bypass pedal, Duhvoodooman's Sonic Tonic (Maxon SD-9 clone +), Voodoo Labs Superfuzz