The head shim works like a head shim. I’m not sure how a copper head gasket 'works' so I don’t know how a mild steel head shim can work like a copper head gasket. I just assume you use a head shim to reduce comp ratio? what else does a copper one do apart from seal on it's own?

Copper is expensive, and cannot be laser cut by the laser cutters I have spoken to (unless the order is worthwhile). So I’m not keen on the $180+ price tag.

ACL head shims at 1.5mm thick cost about $110.00, datsonovic has had a bad experience with one of these corroding badly on his 280. I need something thicker than 1.5 anyhow.

The tube of hylomar I bought was about $15.00, the head shim being a trial piece cut from off-cut material (with minor surface rust) was less than a quarter of the cost of what I was quoted for a copper head gasket made (even tried off-shore for the hope of a cheaper price).

Stainless steel? It’s a matter of cost. I don’t think the mild steel head shim will corrode, not if everything is kept in check. Either way I’m pulling the head every now and then to keep a close eye on it.