My buddy and i just swapped his motor from his 86 to his 90, and he added a 1" phenolic spacer... he had to say goodbye to his strut tower brace. it was about 3/8" too tall to clear the strut tower brace
i have a 3/8" spacer. its makes a very noticable effect as far as upper intake temps go. after running the car car the upper manifold is cool enough that i can bare hand it without being burned. i have a sc now so dont really know what the effect is. i have to use it though or my valve covers will hit
1" space here on trick flow track heat heads, I agree with the upper intake being cooler, also I doubt a stock hood will accomodate the extra height, I have a stormin normin hood and it just about hits the upper intake in the back corner. Also the strut tower brace is a no go.
I am running a 1" spacer on my trackheat intake. call me lucky but it fits under my stock hood but only by a hair. Since I didn't have it without the spacer I can't tell you if it improved the performance.
I ran a 3/8" spacer on an Explorer intake. No hood clearance problems, and the upper definitely stays cooler. The spacer improved ET on a hot lap at the drag strip by 2 to 3 tenths. With the spacer, I could get two back to back runs that were very similar, without it, the second run would always be much slower.
One note though, if you did not block the EGR passages at the heads, or run non-emissions heads, the spacer won't help much because the gasses in the EGR system will heat the upper intake significantly.