From my experience with the sideways carbs I bought the floats from Pro Systems but a lot of carb manufactures have them. The ones you show should have a left and a right taper towards the back of the car. Once you have the correct floats and have them set correctly I'll bet a million dollars it needs bigger shot of fuel at the hit. Small tube nozzle type squirters (31's) with a bigger cam (Squirter cam).
Are you leaving wit your foot on the floor or partly down then full throttle? Hi, I've ordered the wedge floats from quick fuel, we have already "upped" the squirters to .063, these are 1150 dominator carbs, yellow cam only 2 pos'n. We've also upgraded the fuel lines to one size bigger everywhere. We're not back out with the car until the end of August. Footbrake, Launch around 1800rpm. 
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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