Yes it will work the block bolt patteren never changes from 350 to 350. You might run into a problem with a intake manifold not going on though unless you have it too for the heads you want to use.
These should be double hump heads. They are very sought after heads.
small block
Cylinder heads can be bought in bulk from Sportflo in South Africa or try American Cylinder heads if based in the US. For other buyers try Bridge Cylinder Heads in Cheshire, UK.
The lifters are in the cylinder heads.The lifters are in the cylinder heads.
There are two cylinder heads on a V6 3.1L engine.
you can find that type of information at http://www.mortec.com/
A single overhead camshaft engine can have either one or two cylinder heads. The "single" indicates the number of camshafts per head, not the total number of camshafts.
This number will tell you what year and what moter the heads will fit.There are books put out for this purpose.
I was unable to find that exact number at mortec.com, however if you have a set of 3991492's, they are very possibly a set of 70-up LT1 camel hump heads with 64 cc chambers. These would be valuable heads.
3998993 is from 72 or 73 307 or 350. 75 cc chambers.
The 4 cylinder has 1 The 6 cylinder has 2
There are ( 2 ) cylinder heads on your 4.0 liter over head valve V6 engine