Disappointing dyno results

Stock 340 was .429, .444 w /.210 and .220 duration and produced about 275 hp and 340 lb. ft.
You are pretty close to stock but there is something not quite right...you should be up about another 45.
I don't think the problem is cam selection. Give us the dyno details and compression height?
...you have duplicated a lo compression 340 numbers?
Big valve "O" heads, flat top JE pistons with 2 valve reliefs. Calculated 9.687:1 compression, dynamic at 11.103. cc"d at 65.6 Compression check at 150 after 5 revs.
Did you consider head gasket thickness. That makes a difference.