If it is an '88 (possibly 86 or 87) or newer 258 it should have the same 1/2" head bolts as the 4.0 head. good source for the bolts
www.headbolts.com
L6 4.0 liter head bolt set 86 to 96 yrs 1/2 inch bolts chbs-1128
If it is has the 7/16 head bolts Summit racing carries sleeves, I don't know the part number, that would help align the head. You would use 4, one on each corner.
Don't forget to plug the water passages on the drivers side of the head. I used epoxy and have not had any issues with them leaking. Find the water soluble peanuts to temporarily block the back of the passages when putting in the epoxy.
You can use the 258 intake but will need to use the 4.0 exhaust manifold. The stock one is sort of OK but prone to cracking. I ended up using the Borla header.
