Hey guys, I was wondering what type and size of valve spring to use in the axle slip yoke so I can eliminate the C-clip. If someone can point me to a tech article or tell me I would appreciate it.

John, et al;
I just did this.  I also upgraded u-joints to 5-760X, alleged to be 20% stronger than 297X.  Further... I had the axles machined to accept full-circle clips.  Time will tell if this helps at all.  I will end you some fotos.
As far as the spring... I got a used spring from a cat diesel.  Actually, as it is cut down so far, length doesn't matter.  Any spring that fits the diameter well will do, and I am sure any shop that does rebuilds or valve jobs could provide several to test.
Length is critical to avoid both slop and excessive pressure.  I heard 3/4" to 1 1/4" lengths... I think 1"-1 1/4", but definitely no longer!

When doing this on an '89 F-250 front end we used the valvespring from a 302 and cut it to a little over an inch in length.

I use a chevy small block valve spring.  You cut it down so it's about 3/4" or 1" long.  But, you do it to get a certain fit.  After you put the spring in, you want to have to push the spindle 3/4" to seat it on the knuckle. Start at 1" then check and cut down as necessary.  You need to tack weld the yoke cap tho.  I think alot of people aren't doing this and they are gonna find it missing soon.  If you don't know what I'm talking about then visualize this.  The axle slip yoke is like a cup.  The bottom of the cup on the outside is directly facing the Ujoint.  That bottom is only pressed in and will pop out.  You need to tac the bottom in a couple of places to keep it there.

Subject: Re: D44 C-clip elimination
Date: Wed, 21 Aug 2002 09:22:33 -0700 (PDT)
From: "Muddtanks.com" <muddtank@yahoo.com>
To: bigbroncos@moab.off-road.com

Helpful hint: I weld a peice of steel (round and ground) to the inner side of the slip-yoke to keep the spring from punching out the pressed in peice of metal there. It's
punched it out before, but no more.