Yesterday I swapped in a 5.12 samurai front 3rd into a front axle and also installed a hybrid rear housing into my 87 samurai. I have a 3" spring under lift but today noticed the rear driveline extended some. Im all new to this so my question is, do I need a driveline spacer and if so what size do you guys think?

Maybe a 1" unit at the t-case would help.

Disregarding the money aspect, you would be better off getting an extended slipyoke from one of the vendors.

The benefit being that the extended slipyoke would increase the distance between the u-joints at either end of the driveshaft.  This, in turn, would reduce the operating angles of the u-joints.

Yes, the change in the operating angle would be borderline-microscopic, but every little bit helps!

IMO. unless your over mid-way on the splines leave it alone. maybe jack up the frame and let the rear fully drop then
check spline engagement. bottoming out a drive line is never good, it only breaks stuff.

thanks guys I really appreciate the input.

ack: talked to sean and dan at lowrange and I will get that extended yoke probably as dan has one with his 4" or so lift and likes it but when I put in a front sidekick 5.12 third in the front the driveline wouldnt bolt to it so I put on the samurai flange and it was loose and so im going to have to get an adapter from lowrange on that and then afterwards I will get the yoke.

Talk to low range and see if you can get a new flange with both bolt patterns.  Or take your good flange into a machine shop and have them drill new holes for you.

when I put in a front sidekick 5.12 third in the front the driveline wouldnt bolt to it so I put on the samurai flange and it was loose and so im going to have to get an adapter from lowrange on that and then afterwards I will get the yoke.

You should have just drilled the smaller samurai bolt pattern into the trackick flange.  No machine shop or specialty tools needed (just a drill and the proper sized drill bit).  You just use the samurai driveshaft end as a template for marking/drilling the holes.  The driveshaft end self-centers on the trackick flange, then you just clock it so the new holes are approximately halfway between the old holes.  I've done this to several trackick flanges and samurai large pattern tcase flanges and have not had any issues with vibrations or anything else.  Once you get one hole drilled, go ahead and put a bolt and nut through it and tighten it up, that way it keeps the flange in place.  Then drill the next hole opposite of the first hole...bolt and nut it too, then drill the last 2 holes.