Considering a replacement for my stolen 69. Car has partial quarter panels installed. Install looks clean to a laymans eye but I am wanting an opinion from someone who has used them. Do they hold up? More prone to crack if I happen to drop-in a stroked BBC?

Thanks in advance for any replies.

If they are completly welded in and not spot welded on the seam, the WILL last just the same as a full quarter. They are after all "melted" together and ONE after they are welded.

If it is spot welded along the seam that will likely fail to a certain degree, how much, it is hard to say.

No motor is going to make a difference, if the body work is done incorrectly, it will fail with a six cylinder or a blown big block, it doesn't matter.