More T98 Questions

Okay, I've been reading through old threads all day and I still have a few questions that I wanted to get confirmation on. I've found a T98 with the D20 still attached and I'm trying to decide how much work I'm getting into. I have an L-head so it would need to fit up to that.
First of all the input shaft. The one on the transmission (from a 66 J-truck) is long. I know this would need to be replaced or modified. It sounds like using a short T18 shaft is not possible due to internal gear differences. Is this correct? Are "short" T98 input gears still available? (I know that even a "short" T18 or T98 input shaft will not bolt directly into an L-head unless it is the elusive F-head T98 shaft.) What about having the shaft machined down? Any idea how difficult and expensive that would be?
Second, the T-case. The D20 has a centered output. Can I take my current D18 and bolt it up to the T98 without any issues (that sounds too easy)? The adapter plate is already there. Are the gears the same or would I need to change something internally?
Third, overdrive. My long range plans involve an overdrive. Can an overdrive still be used on these? My assumption is yes but I wanted to confirm before I wound up purchasing a transmission that I would only want to swap later. As far as the overdrive is concerned is there any difference between T90 and T98?

Thanks in advance,
Stephen

 

Stephen here is what my thoughts are:
I have no experience with the T18/T98 other than parts manuals; I am thinking out loud here.
When swapping a F4/L4/T90 to a V6, we use the longer T90 6 cyl input shaft with an apapter. T90s are 3 speed transmissions.
My thinking is, why change the shaft? couldn't an adapter be purchased/made for your longer shaft to work with the 4 cyl bellhousing? More knowlegable people will let me/us know that answer. Cost and driveline length issues also.
Your D18 should bolt up; keep in mind the 2 different input gears, the ones that bolt onto the trans output and drive the transfer case; 26 or 29 tooth are possible here.
The Warn/Saturn overdrives bolt to the transfer case; 26 and 29 tooth here also; so once the other 2 problems/issuse have been solved, the overdrive will work as well.
Good luck on your project!

 

So am I right in the thought that you can't swap "some" of the T98 parts with T18 parts? This is an all or nothing proposition correct?

 

You can swap T-18 guts into a T-98 case and vice verse, but you have to swap ALL the guts. You cannot mix and match the parts. The rear adapter you have will work fine but you have to have a large hole 18 transfer case because the adapter you have is set up for the large hole transfer case. If you have the small hole transfer case you can put the 18 guts in the 20 case with no modifications. It's the same procedures as if you were rebuilding the transfer case. Just for informational purposes, all 20's used the 1 1/4" intermediate shaft, but there were small and large hole 18's with the 1 1/4" intermediate shaft. When we say large hole, we mean the indexing hole in the transfer case that aligns it with the transmission output shaft. The T-98 should be a 6 spline output shaft and you will need the 6 spline input gear that matches your transfer case. You cannot use the one that came with the 20 as the pitch of the gear is wrong and possibly the tooth count.

The biggest problem is no one makes the adapter and input shaft aftermarket. That's why I got the input shaft from Dan. We are still working on this, but money has been a factor recently. You might try Herm as was mentioned. Sometimes he can come up with those parts. All you should need is the input shaft and the front adapter an front bearing retainer. Nickmil.