wow a shop that sells heads told you to buy new ones... i can hardly believe it
the 317 heads are identical to the ls6 243 heads except combustion chamber size, if you send them out to a reputable shop (not TSP or patriot) like total engine airflow they can be CNC ported to flow like or better than a new set of aftermarket heads, and support 500 rwhp with a decent cam, with NO other changes... besides many of the performance heads you buy are cnc ported OEM castings unless you want to shell out upwards of 3 grand for a pair of CNC ported AFR's...
6.0L Stage 3
Lift Intake Exhaust
0.1 70.6 50.4
0.2 143.1 118.2
0.3 210.9 186.7
0.4 261.1 230.7
0.5 302.9 260.1
0.55 319 269.4
0.6 334 277.1
http://www.totalengineairflow.com/pr.../gmhead/gmls6/
another option is to not remove the heads at all (it will cost you a set of gaskets and cylinder head bolts to do so), and only replace the cam, installing for example a texas speed and performance tsunami MS3/MS4 cam will gain you over 50Hp and have a great musclecar'ish idle.. it costs about 700 USD for the cam, springs and pushrods, you will have to change the springs with the heads installed but it is the cheapest route.. and it will net you a 450+ hp engine for very little money
texas speed also sells heads that are cheaper than the TEA's but the quality of the work just isnt the same...
as for inspecting the bottom end, its a waste of good money to do so, you will drop the oilpan to change the cam and if you want to spend some good money you change to ARP rod bolts, that allows you to inspect the rod bearings (and they are never worn) and visually inspect the bores (they are also never worn) only thing you have to remember is to change the oil pickup o-ring... it costs about 2 dollars and it can (will) make a wierd sound if you dont... some people also swears by a ported ls6 oil pumo at this stage...
http://www.texas-speed.com/shop/cate...MID=5&catid=44