a 1/2"-3/4" wide strap made of 1/4" thick steel would hold it in. I dont think i would rivet it in, i would tap the block and use 1/4" bolts to secure it with some sealant on the threads to keep them from leaking (since most likely the bolts will protrude into the water jackets)
i have taps if you need to borrow them.
Find one of those liter cars with as much room as an american car at near the price on our market. Most people could give a shit less about a fast liter car over here. Something that small should be cheap and get good fuel economy. If we want to go fast, we buy something that is actually fast.
People paying that for american cars over there are doing that for a reason. They can. Just like people that buy expensive imports here.