First of all it depends on what school you are aiming for an if you are in catchment or not.
Check out the traffic light doc available on the CSSE website that gives you the standardised score needed for entry to each school. The lowest is 303 for in catchment.
Then, take a look at this thread which will give you an idea of how last years raw scores translated into the standardised score. As a rough rule of thumb 80 out of 120 across both tests seems to result in a score comfortably above 303. viewtopic.php?f=15&t=44119
70 out of 120 is still a pass but is getting a bit bum squeaky.
It seems to fairly traditional for the English to be weighted more heavily than the maths, which is good news for you as it will up your standardised score, but I believe the standardisation is calculated every year depending on how the scores for the tests are distributed so it is going to depend on how the rest of the cohort perform.
Where do you live and which school(s) are you intending to apply to? The priority admissions area for the Southend and Westcliff High Schools is anywhere in postcode areas SS0 - SS9 inclusive and these are the schools for which the standardised score of 303 is pertinent. A score of 303 or more will get you a place so long as fewer (or the same number) apply from the priority area than there are in-catchment places available, but not necessarily at your first choice - SHSB tends to be more popular IC than WHSB, for instance. Looking at the girls' schools, I think there is less of a disparity, however, although where we live is closer to WHSG, quite a lot of girls choose Southend, including our DD. ColCHS has no priority admissions area and admits purely on score.
The two papers are weighted equally. The difference in the effect that getting one question right or wrong in English compared to Maths will make will be due to the mean raw score and standard deviation being different for the two papers. (Of course, by chance, there may turn out to be the same for the two papers, but it is unlikely). My memory is that 36/60 in both Maths and English last year did not quite make a standardised score of 303, but I may be wrong.
BTW the range of standardised scores achieved for each paper will be something like 69 - 140, but the combined score for the two papers is multiplied by 1.5 to give a range with a Southend pass score of 303; I assume they decided to do it like this because for years people had been used to seeing scores in this format.