I have a 71 LeSabre convertible. I would love to swap the 350 out for a 455 because she's a big girl and could use a bit more power. I have no idea where to get a 50 year old 455 or where to start. Any advice?
You are in the right place. Let us know where you are as shipping engines isn't so easy (still doable). There is a parts for sale forum also.
Start right here. Try to find a 455 w/T400 trans. You will also need the frame brackets / motor mounts. Some exhaust work may be needed. Trans cross member may need to move some. Driveshaft may need to be shortened. Radiator hoses may be different. Engine wiring harness will be a little different. Perhaps keep the 350 and put in a performance cam and tune up with a good trans shift kit - at least until the Fall/Winter.
Step 1: Find the 455 motor and tranny 2: pull the old 350 and tranny 3: install the 455 and tranny 4 Enjoy the BBB experience But seriously, make a checklist first to get everything you need before you start to make it as painless as possible, nothing worse than waiting to find a part you need and stalling the process.
I let two '71 long blocks go to scrap 2 1/2 years ago. Both were from large cars. Local mom/pop yard crushed out. Probably should have made more of an effort to save, but am simply too far from potential buyers.
I'll throw this out - why not build up the 350? Unless you simply want to install a stock 455, you are going to be building up a motor either way. And you'll save yourself the extra work of getting the 455 installed.