Im looking at plenum spacer but apparently there are three sizes 5/16 1/2 and 5/8. I am looking at the thicker ones 1/2 or 5/8 but am worried about if the strut bar will still fit.

 

only the 5/16" fits under the strut bar.

 

The plenum spacer should come with spacers (aka washers) to install under the strut bar mounts so it will clear if you go larger.

 

This. My motordyne came with spacers.

 

Aka "fender washers"...
You use these to shim the brace a little higher, the bolts are plenty long enough.

 

I thought the spacers were for the 6 bolts in the middle (inside the plenum)?

 

Stack the washers at the four mounting points on each shock tower to raise the strut bar off the plenum.

The plenum spacer should have also come with longer bolts to account for the spacer. I believe mine came with some rubber washers to seal the upper plenum.

I wasn't quite satisfied with the OEM bolts so I went with some longer ones. I used M10-1.25 X 30mm J.I.S. Small Head Hex Flange Bolts and reused the nut on each side.

 

both ...

if you ask me tower brace spacers are jank as hell! If I saw these installed on someones car I would think less of them and their build.

 

Lol, this is one of the many reasons I swapped to a velocity manifold, and also have the Carbing brace.