No start on rebuilt 360LA

Recently rebuilt the motor from the junkyard. Had cylinders bored .030 over. KB107 pistons, stock crank/rods. Comp Cams XE .525/.525 cam. Rpm Performer heads, comp cams roller rockerS, RPM Air Gap intake, Holley 750 DP carb. Outside motor: MSD Magnetic pickup/mechanical advance distributor, -6AL MSD Ignition box, Holley electric fuel pump (regulated to 7psi) battery (relocated to trunk via summit racing kit) summit ignition switch panel.

Turns over smooth, getting fuel, all tolerances/torques checked. Timed +- 10 degrees. We are getting backfires but no start.