ok, ive been lookin at an h22a engine that has about 30k-45k on it. can i roll the odometer back accordingly? or do i just keep track of engine mileage on my on? any info would be appreciated

Legally, you never touch the odometer. If it were meant to track engine usage, you would track hours the engine is running (Like commercial equipment does). Note the change in the records of the car, but you cant change the odometer. I did a couple RX-7 engine replacements and just tracked the additional miles on the engine, and when I sold them, disclosed both numbers