4.2 to 4.0 head swap

[Bowbrother]

My brother made me a gift of a 1985 CJ7 that hasn't run in years. Brother bought it during the early 1990s and has done no engine mods. The engine is a AMC 258 i6 / 4.2l but has a Clifford intake with a Holley 4 barrel. My question is how do I determine if the 4.2 (258) head has been swapped for a 4.0 head.
Any help here would be appreciated.

 

[Lumpy Grits]

:ww:

Can't help you with the head question.

'85 CJ's didn't come with a Dana 44 rear axle.
Is the rear diff cover round?
LG

 

[DaveMueller]

The 4.0 head is wider in spots, you need to plug some of the casting holes in the head with epoxy since they're in the water jacket. I think on the manifold side. Check for some serious overhang of the head.

On the AMC 258 i6 / 4.2l heads, the intake and exhaust manifolds are in line. I think on the 4.0 heads, the intake sits lower and should be obvious.

A compression check would show higher than expected numbers.

I think there were other minor differences like location of temp sensors, type of thermostat housing etc.

If all else fails, pull off the cover and check the casting number.

 

[hole]

A pic or 2 might help us out

 

[Amiles42]

I have been thinking about doing this swap, I have done a ton of reading and think that it would be the most efficient upgrade I can do. Has anyone used this supplier?

https://www.alliedmotorparts.com/91-95-jeep-4-0l-242ci-120-cylinder-head.html

 

[hole]

There are companies that will weld the water jackets/ports closed for this swap.If it was mentioned on the website you linked, I missed it. I used Clearwater Cylinder Heads