Big Red 300es questions
Hi guys so a few years ago i picked up a trx 300 2wd motor in hope to put in a big red. After further review the engine was toast and would need alot of work. Fast forward to today, i was at school looking at kijiji and saw a guy local 
that was parting out a 1990 trx300 with a 2wd engine in it. So i called him and bought this for 100 bucks, came with the carb and throttle cable.
Do i need the complete 300 wiring harness. I understand that i will be swapping out the output shaft with the 250 but im looking for some feedback as to what else i need to do to get the most power out of this baby.
Another question: While i am going over the 300 motor, can i stick the 300 carb on my 250sx without re-jetting? any difference?
85 250sx
86 300es in the making
86 200x
86 350x