alternatives to an 8.75- what about an explorer 8.8?

You will need new spring perches, even if the stock perches were the right width the pinion angle would be off anyways, the shockmounts are on the mounting plates so no change there.
If you currently have a 7.25 you will need shock mounting plates from a mopar with 3" axle tubes - pretty much any car from the 60's-70's is game as long as it doesn't have iso springs.