4 things for motor to run.----Spark ( 1/4" gap ) at the right time.----Correct amount of fuel.----Compression.----And compression in the crankcase.------Simple inspection / testing needs to be done.-----We are at post #74 and counting.
Judging by the pictures that Mercury needs a complete teardown / inspection / evaluation.-------Not going to run like new with just a fresh tank of gas and a new battery.
????---in 77 the parts book shows a 32 inch block for the 25 HP.-----There may be some 22 cube engines in 77.-----Only with more pictures can we tell what you have here.
I think looking at the parts manuals found on line , you can help yourself.-----I often post answers that are deemed suspect by novices.----Sorry to be blunt here.