In all honesty, a big block is NOT the way to go. With the cost and time of modifying the mounts, clutch, chasis, exhaust, etc you can get a better .12 or .18 for less money and less stress.
I can't remember much on that RS4 Racer (is it set up for slide or rotary carb?)or know what kind of budget you're working with. If you're not planning on racing, an OS or LRP .18 sounds right up your alley. IF you do want to race, there are plenty of .12s to fit your budget.
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