I'll chime in here.
ALL my GMC's using the stock oil pumps had swinging pickups; I've had 20. I never, repeat never had an oil problem with this setup. If you are going to use the stock pan I suggest hinged flappers over the drain back holes in the braces as all the oil wants to go to the timing cover on deceleration and I guarentee you will loose pressure especially at Bonneville without them. I would also suggest a welded angle scraper on the side of the pan if you are not going to make one which will attach between the engine rail and pan. There is a 12 quart pan and a 7 quart pan; the bottom of the pump are the ony difference. This does not include the military 4X4 pan.
The 270 has a lot more "meat" between the bores so it is a possibility you may not have gasket problems. Check with "Best Gaskets" for your 270 it may be the answer. I have tried everything to hold back high compression on my .060" over 302's with only one thing working. Remember high compression is like a blower both putting strains on head sealing. The best for me was a .040" o-ring in the head and a.040" o-ring in the block pushing against a stock gasket. I promise you I tried every other comination of gaskets and o-ring/reciever groves without success. O-ringing a head is time consuming and needs a custom fixture unless your machinist is really good using a head gasket.
The only time a copper gasket worked for me was with the Skinner 12/port and it had a .050" o-ring and a reciever groove and .060" copper gasket. The only reason it work was we added 2 more head "allen cap screws" in the water jacket between our problem cylinders.
Doug Robinson went to 9/16" head studs to hold on his blown stock heads. Oh yeah head studs are a must. APR will package them up for you. They MAY now list them for a GMC 302; when I first asked for them they didn't. Remember the hardened washers and nuts.
Stock rods will be plenty good but make sure you have enough side clearance to let out the oil and change the nuts (ARP again). My stock pumps, when I ran them right at 50 psi with a little bypass work. Remember to oil your distributor gear.
If the head you are going to use has two 1/2" water plugs near the back, the front one is for your water temp guage and rear one is to be plumbed back up to the left side of the thermostat neck. This is a must for hi-comp and blown GMC's that back cylinder head and block gets mighty hot and that flow back hose is stock on military 302's to control this.
Roller rockers are hard to come by (I made my own) and if you go over .500" lift at the valve you can have the stock rocker continually pushing the valve back and forth causing valve guide wear if you don't have the geometry just right. Working with the rocker stands and lash caps can help with this. Smith Brotheres and Manton can make push rods; I have used both.
I hope this helps. Just stuff I've learn with GMC over the last 50 years......Good Luck JD
