I've heard of people using 20w50 engine oil to stiffen things up.
I couldn't find anything in my service manual about what oil to use but I think from memory its 30w. Could be wrong hopefully someone else will chime in
genrally standard they use a very thin hydraulic oil(10-30 or lighter), ive fitted engine oil in the past and its worked almost too well... feel all the bumps but the car handled well on the track... its cheap but i wouldnt bother as gas ones are well priced..
as for anti freeze i know alot of circuit guys use it in the strut around the insert as this helps disapate heat. very effective so im told..
i cheat i use motor cycle fork oil will try and find the container find it is the best but then again uim a cheap skate as i had a 4 litre pack given to me