Wanting to swap a RRC 4.2L into a '90 with a 3.9L

I found this explanation from a post back in 2007 from Ken...

"Everything will work but you need to swap the timing cover from the
3.9 to the 4.2 unless you prefer the serpentine belt. I used the
intake from the 3.9 as well and the exhaust manfiolds for the 4.2.
Distributor from 3.9 as well. I will be remapping the ECU after
getting a Mallory Distributor for cleaner more reliable ignition. Then
I will be done and ready for installing an LPG set up. But that is the
direction I am going. As it is now with all RR parts ( except an
electric fan in plave of the clutch fan ) I am very very very happy"


Can anyone else confirm/deny this report or care to add any additional information for me?

I'd like to have my ducks in a row before rolling this thing home...

 

I would not do a motor swap with anything other than what it came with unless I had a bunch of time and money. I would just source another 3.9 since they are cheap and around and just do the swap and be driving it. I know there is a 3.9 with less than 99K on it here for $400. Just my .02

 

Well I've got the time and the backyard for the project. Not looking to dump much money into it at all. The owner of the 4.2L has money and its just been sitting, so I think I can get it for quite cheap. If I can't, then yes, I'd source out another used motor as I'm not looking to drop a new Turner Engineering into this beast. If it was in great cosmetic shape inside and out, then i'd consider new, but its clearly not.
I might even consider doing my first motor swap just for the experience, but if not I've got a friend that can give me a good price.

We will find out soon, the owner is supposed to call me tomorrow to finalize the deal, we'll see how cold his feet get, but his girlfriend bitchin about it being in the backyard is on my side!

 

It really depends Brandon. If it just needs a new water pump and a top end rebuild... I would still consider it worth it. These engines (especially the classic) are easy to work on. Like I said, it really does depend on what you want to do with it. If you don't mind it sitting around for a month until you get things in order to fix it like Rob said. Then I would consider it an excellent buy. If it were here locally, I would buy it in a heart beat. Until you have narrowed the engine problems down, I would not consider an engine swap unless it was a last resort.

 

Agreed, I was going to just grab it and clean it up and do some pressure and compression tests before I did anything else. But the seller who's had this thing sitting for many months and not listed anywhere all of the sudden had another buyer and tried to get me to pay more the day I was supposed to pick it up. I told him good luck.

I've been wanting an RRC and have had an "eventually plan" that I will put into action before too long. For now, I can focus my attention back on my D1 and get her in tip top condition...and when I say tip top, I mean good for 14 years old and not spending a bunch on it!

Thanks guys for the input, hope to join you in the RR world someday.