I'd say it's not impossible if you work hard enough, but it's unlikely. This also depends on what you mean by "pretty well" due to the scaling.
A lot of the content is building on from the 1/2 such as complex numbers, vectors, and mechanics (as well as the 1/2 being assumed knowledge), so you would probs have to do a fair bit of work to overcome this problem. However, the content from 1/2 itself isn't too difficult, so maybe you should look over what's relevant from the 1/2 and do some chapter reviews from the textbook??
I know one person who did do the 3/4 without the 1/2 and scored a 29, scaled to about 40, so if you're happy with that, a good score is possible.
Additionally, if you've already completed methods 3/4 you would be better equipped for spec 3/4 without the 1/2 (especially due to the probability and stats topics).