Rear End Fishtail

[Chevypoor]

Alright lets get the laughs out now, yes I am having some traction issues with a 305 sbc. For the last 7 years I have been running a peg leg doing the one wheel peel. After adding ball flange collector extensions to my headers and an x-pipe the one wheel peel started happening from a rolling start at say 20 or mph. Went to a posi and 3.73s thinking that would help. Now out of the hole she will hook fine most of the time. However with no power steering I do alot of rolling starts when turning left or right. Once I am almost straight probably going 10-15 mph I will lay the wood to her. Anymore than 75% throttle and once I hit about 20 or so about 4000 grand, the rear end will fish tale side to side and will not stop until I let off or shift into second (manually shifting a turbo 350) at 60-65 mph. Sometimes it is bad enough were the opposite lock is not enough to ride her out. Running 275 60 r15 on 8" steelies in the rear, Early Classic trailing arms, stock ride height, 34psi in the tires, polyurethane track bar bushings, Rancho shocks, one coil cut in the front. She is a long box with a 22 gal plastic cell passenger side of the box about a foot from the front of the box. Do I need more weight in the rear or a shock change? Should I move the fuel cell to dead center over the rear axle? I am planning on relocating the battery to box soon. Looking for any thoughts or help from you guys!