Oil Pan Gasket Issues

[1968CHEVYC10]

the rear main seal was leaking pretty bad on my 350. According to my suffix code the block is a '75, but the gasket they gave at oreilly's didn't look like it was the right one, it looked like this: http://www.autozone.com/autozone/par...74451_0_12292_ (the oreilly site was down but it's the same part) There should've been only one of the two larger holes on the sides, for the dipstick. So I took it back and they gave me one for a '74 350 that had it only on one side. Anyway I got it in put oil in it and now it's leaking way worse than it was before, especially bad at the front near the timing cover. I've heard that GM changed the thickness of the gasket where it meets the timing cover in 81, but also switched the dipstick to the other side. Anyway I'm just wondering if anybody has had this problem and how they fixed it. Thanks Yall!!