SO I'm thinking of getting a trac-loc in my mark at some point - which do I want. I have no idea how many splines or anything like that except I need one for an 8.8 rear.

IIRC it's a 28 Spline.

You need to get the one for the irs diff, either one out of an irs or a newer one will work. I can't remeber the year you need, but if you buy new it will work.

Yup 28 spline and either buy new or make sure it's one for an IRS car. I got all my stuff from Max @ Five Star Ford

4.10 + posi = happiness with a mark viii

I just sold my 4.10 posi, total build cost about 950.00. I wanted to go down any way to a 3.73.

Thank you for the referral Rich..
New trac loc 184.00
new brg kit 78.20
new 3:73 gears 144.00 ......labor ...priceless (always wanted to say that LOL!!) about 4 hours.
total parts $406.20 your cost plus shipping..all ford racing parts

Max

ANY 8.8 unit will work, it does NOT have to be for an IRS. TRUST me.

I do not mean to dispute what you say but not all 8.8's are created equal....older side gears did not have the chamfer so once you put the irs halfshaft in you could not pop it out from the out side...right?? All irs 28spline are the same but the solid..live..axles are not always.

ANY 8.8 unit will work, it does NOT have to be for an IRS. TRUST me.

they don't have to be for the IRS it just makes work on them ease go here to see the differences
http://www.lincolnvscadillac.com/showthread.php?t=36811