i have some pics of my heads and i have some pics of heads other people have ported off of here.ive heared that the 342 casting are thicker, and thats the casting number im running, but they seem about the same as the later heads ,imo. the lt4 heads are thick in the port and bowl area. all aluminum lt1 castings are about the same.

i would get an asortmant of carbide burrs for cutting aluminum.youll get mad with those cartrige rolls and sanding drums,they work great fpr polishing,not so much for removing material.also get some machinest dye for marking gaskets and port walls.coat the entire port with the dye, from valve to gasket and then grind all the dye off.do this 3-4times for the intake 5-6 for the exaust .this will enlage the entire port uniformly.

then you can concentrate on the valve pockets and areas where the runners make a turn like in the intake ports where they make a turn around the pushrods.stick your fingers in there and pintch the port walls to judge the thickness.3/16ths is too thin,but in some places its only about an 1/8 thick, so be carefull! your time will be best spent in the valve pocket area,smoothing the edges and making the whole pocket area bigger maybe 3 more passes with dye and grinding it off.make the area where the valve guide sticks out into the valve pocket smaller.use carbide burrs on the aluminum and grinding stones on the guide material. the exaust will need more help than the intake, and the walls need to be a little thicker to held guard agenst cracks with the extra heat the exaust makes. the bottom of exaust port is realy thick,it goes all the way down to the deck, so grind the most off of the bottom of the exaust port.another area that realy hurts flow is the sharp corner going into and coming out of the valve pocket.try to make that a stright shot. try to give the gasses a stright shot to the valve on both the intake and exaust,without making the port walls too thin.good luck! you can do it,just take your time.one port a day after work, just go slow.wait untill after porting for the valve job, just in case you get into the valve seat on accedent.
im sure you know about gasket matching, so i wont get into that much.just makesure the port on the head is a lil bigger than the intake.ive peeked down into the intakes with a bore scope,and things never line up perfectly in there.also if you have to cut a lil off the gaskets to make sure they dont hang over into the ports then do so.trace the gaskets with dye and smooth that gasket patern into the port.