This is why they sell the kits IMHO.
They do all the homework, and you weld it in. There are a LOT more things to dial in on a 4 link than anything else.
I would recommend going over to Pirate4x4.Com - The largest off roading website in the world.
and reading on there. They also have some anti squat calculators and such.
To be honest, and please do not take this the wrong way, if you are trying to figure angles and link length out, I do not think you are ready yet to do a home made 4 link.
Pretty much all the successful home made 4 link setups I have seen in person, went into the cab area on XJ's. There just is not enough room under them for the length of links you need.
Please go and do a LOT of research BEFORE starting this, as done wrong it will be a death trap.
may I also ask why you are dead set on a true 4 link rear? For a fraction of the cost, even doing it all yourself, you can have custom leaf springs made that will ride like a dream.
1998 XJ on 37's.JK Rubi axles with chromo shafts and ctm's, 4:1 transfer case, etc etc etc.The Cherylkee....
2003 Range Rover HSE, 4.4 Quad Cam.
1998 Range Rover 4.6 HSE
2000 4.7 4WD WJ with a rebuilt motor.
4.3/700r4/new frame buildup (YJ)....
Years to gain the hands on experience, and offer it freely.
Minutes to gain the knowledge from the internet, and quote it just as freely.