340 No low end power

Need some guidance, picked up 68 Dart and it has no low end power. Runs great, great top end but no launch at all, if I power brake it can’t break the tires loose and it seems to maybe rev to about 1200 rpm at best. The few times it did break loose it was like being on ice, burning the tires off like you would think it would. Here is what I was told when I bought it and what it has.
Was told.. Fresh rebuild to “sixpack specs” mopar purple cam and 72 360 heads 1.88/1.60 valves. I had the manifold off and it is a purple cam but don’t know the specs. Suppose to have a stall converter and shift kit but specs are unknown.
It has.. Torker II manifold, carter avs carb, Mallory mechanical Unilite dist, Mallory voltmaster coil, autolite 66 plugs, look a little lean to me, Hooker comp headers, 3 inch x pipe dual exhaust with magnaflows, 727 reverse valve body and 8 ¼ suregrip (no tag don’t know the gears). Timing set at 13 btdc but i dont know the total. Not sure where to start or if I am expecting too much from it