is a conversion like this prone to failure? i am not sure what they did to achieve this increase in displacement but it makes me a littler nervous as not sure how much you can increase the bore and what to look for as a sign of compromised engine integrity

If you read up on big bores, the consensus is, heat kills. Make sure her cooling is optimum and she should last quite a while.

I just grenaded my 2258 on the track by losing an exhaust valve in the chamber.

The build was 22 years old and had mostly track miles on it. They can be built to last, just need to take care of them. I run a FAT 911 fan system, 6 fender tank with oversized oil pump and Mazda front cooler. I was going to break her down after the season was over, but it fell short one race...

There are arguably better cooling methods out there, but I like mine, and with a few tweaks I’ll keep it on the new build.

Some of that increase will come from a larger bore and some from a longer stroke on the crank. Some of the builders I have followed have had great success building large displacement type 4's