easy, take the cowl off and with a straight edge ( i use steel ) find a point on the engine that mirrors itse'f on both sides (usually the ledge that your bolts run through) now from thte back edge of that mounting rail measure STRAIGHT back to the firewall. both sides should be EXACTLY the same. this will put the engine 90 degrees to the firewall so all the thrust you have is whats built into the firewall. on the other side, with lases kits being more common, the chances of the thrust angle being off is remote BUT that is a possibility if you've already checked everything else.