Read Jupiter as being conjunct the I.C. rather than as opposition the M.C.
Read Jupiter as being in the 3rd house because it IS in the 3rd house. Why bother reading a chart if you are going to change it around?
But double-check for how accurate and precise the birthtime is. Just being off by 4 minutes of birthtime COULD change the MC/IC and change the house-location of Jupiter.
This is why a precise birthtime is so important.
But remember that if the recorded birthtime is inaccurate, it is going to be LATER than the actual time ... they right down the time they NOTICE the clock, and I'm sure some nurses are more dedicted to getting the time right and some less so .. especially if there is any medical concern at the time of delivery ... so the odds of Jupiter actually being IN the 4th house is pretty low.
Jupiter is not some magic pill . .it is just how you try to expand your horizons, reach out and network with others. It doesn't "make" things happen . .although optimism and networking DO tend to bring you more opportunities in life.
In general, the planet is a part of your personality. The sign is the general style, but how well/poorly it functions and whether it expresses the positive/negative side of that sign depends on how Jupiter aspects (interacts with) other planets in your chart. Aspects are the most important interpretation tool.
The house a planet is in indicate what area of life you look to, in order to meet that planet/need.