I've got a VK Injected 202 for sale if you want.... I'll let it go for $700 with all injection gear if you're interested..... was rebuilt less than 5000kms ago with a bigger cam and ULP heads....
if he was able to bore his 186 anything bigger than a 192, the temperature will be sky high, not to mention how thin the cylinder walls would be...
if the head flowed well and it had a performance cam, theres no reason why it shouldnt go on a 173.