"Updating" 3.9 V-6

Hey folks! Looking for ideas. Had a 1987 Dakota 2WD. Rear end blew. Picked up a 1994 Dakota 4x4 for a song. (engine had a rod sticking out the bottom.) So, I says to myself, I think I'll put the '87 engine in the '94 truck. Wanted to keep all of the bells and whistles - cruise, injection, etc. ..... So, stripped manifolds, heads, all of that stuff off the '94 engine, put it on the 87 block. Only problem is, the older block had no place to bolt on the crankshaft position sensor. I have been told that the position of the sensor is critical ...tolerance in the thousandths of an inch. Need to find out how to determine exactly where the holes should go, and how best to make them. Help!

Uh, unless my brain fails me, the 87 and 94 blocks are not the same. The 94 is from the Magnum series that came out in '92. You can physically put the new heads on the older block but the water jackets and oil passages aren't in the same place. You may get it started, but without oil and water to the head, it won't last any more than a few seconds. I have heard of people cutting welding and drilling new passages to update old engines to Magnum heads.

Ouch!! My brain hurts!! I could swear that when I put the head gaskets (from a set for the '94 engine) on the block, all of the passages lined up. Do I misreccollect? If I have to pull this thing apart, it is going to become a mooring anchor, and I will throw in a V-8 off of e-bay.

Just do like you said about the V8. Don't even bother with the six cylinders.

So, what gets drilled / cut, block or head? and why did the headgaskets appear to fit the block?

I saw an article in a magazine years ago that showed the differences between the two. The passages for coolant and oil overlapped some but needed to be "moved over" so a proper flow could be achieved. It would make sense that if your gasket was for the year of the block you have, that it would look OK. Did you compare it to the head also? You should probably get an expert opinion also, it may be that my memory is faulty and I'm sending you on a goose chase. The article was from about 10 years ago. I checked my collection but can't find it.

The gasket setwas for the '94 (magnum) engine. That is why I am puzzled that it appeaered to fit the block properly.

It may be that I have brain failure and you are OK with the setup.
If after you get it running, it wants to overheat or has oil pressure problems, you will have an idea were to start.

You may want to look at this website.
It appears the Magnum heads are expecting the oil for the head to come through the pushrods. The non-magnum blocks don't do this, they send the oil through a passage.

http://www.babcox.com/editorial/ar/ar40090.htm

So it looks like I would have been better off if I had used the cam, lifters, and pushrods from the '94 engine, rather than using the '87 cam, lifters, and pushrods. Couldn't use just the pushrods from the '94, as they are shorter. Anybody know of any aftermarket pushrods which would be the same length as the '87, but hollow, like the '94? If so, would that solve the oiling issue?

I don't think you can use the newer cam in the old block, the lifters are at a different angle in comparison with the cam. The lifter valley was changed so the lifter and pushrod are more in line with each other in the Magnum series.