340 on pump gas

I have run a 10-1 iron headed 360 on pp gas before. You will be fine with the current short block combo and iron head. I would use 2.02 valve and port the head.
Otherwise, that cam and the parts you have are good for 400HP.

A cam to match the gears is another story. I would start looking at cams in the [email protected] area with as much lift as the ported head can handle.

A single plane intake, 750 or better Holley and this Comp Cam; http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=633&sb=2

The LD-340 is restrictive to running mid 11's. While possible, make the move to a M1 single plane or a RPM at a min.
It is possible to trade out right for the M1 with the LD-340.