might be handy for someone i tried to get a phenolic spacer for au 5.0 (which has gt40 lower intake ,round ports) had to come from USA worked out to $150 nz (a bit steep ) so rung ar ound and u can get material for around $20 bucks from engineering supply place they use a lot in insulating switchboards , then all uneed is a 44mm holesaw and 8mm drill unbolt upper intake and cut a gasket and transfer 2 spacer material (i used 12mm) hard to find longer bolts so u can cut a bit off bosses at ends of inlet and file smooth ,countersink centre ones . Cant notice any power increase but u couldnt hold ur hand on inlet b4 now u can so its gotta help . oh and if u got ajigsaw helps to cut around the outside

Interesting!
Do you know what this material is called ?
I could do with something like this on my I6, it gets a bit hot and bothered running 12.5:1 compression.

its just called phenolic material there is 2 types and it comes in sheets (not sure of size) i just got some off cuts theres black which is rated at 100 deg its like a plastic see it in carby spacers .I got this red/brown color good for 125 deg its made of bits of wood coated in resin guy said u can work with it just like wood sand and file it etc. i found that the ports top to bottom were about 3mm out of line so u can do that at same timewith a grinding bit in a drill all good fun if ya like muckin around in the garage

If you do this make sure you use the brown stuff as engine temps are normally around the 90-100deg mark and even hotter after engine shutdown so the black stuff rated at 100deg is probably not up to it really. As said its normally known as phenolic or insulation board.

I made my own spacer , but used 15mm alloy flatbar and 1.2mm gaskets on either side, I only done this so my plennum would clear the rocker covers & to block off the EGR from the lower manifold, it seemed to help with higher rpm BUT there was a lot of mods done at the same time when I installed it so ,who knows?

Be very careful with the Phenolic. We use it at work, and we always work it under a spray mist, as it very toxic, to keep the dust wet and we use gloves and a respirator.