'88 5.0 heads?

well first of all, his heads will not just bolt onto your 289, you'd need to change the water passages, but you'd need to do that with most aftermarket alum heads too. those E7 heads flow a little better, but unless you have them milled they will significantly drop your compression ratio, and would most likely cause you to lose power. if you wanted to spend the money to have them reworked, milled and ported, you could make a lot of power with them.

you could use the camshaft, but you'd need to machine the block to accept roller lifters, or use special retrofit lifters ($$$$). if you took his cam, lifters and the lifter spyder thing you could do it pretty cheaply. but more than likely he's going to want to keep the roller cam stuff for his new motor.

30 bucks sounds like a good deal, but when you look at all the work you'd need to do to get the parts installed.... you might however be able to use the heads as cores for some worked over ones, like thumpers, i think he has a $100 core charge.

ethire port your heads or find some 351's
i have both and i think the ported 289 heads are slightly better with what i run

or ya can always go buy some but thats more money