Hagerty member and first time poster here with a question for the masses:
I recently bought a '57 Canadian Pontiac 261 that I was planning on rebuilding. After pulling the head, I found two blown cylinders (likely from not drilling the steam holes in the 235 head). When is it worth having a block sleeved? I was planning on rebuilding this for my '48 Chevy pickup and 261's don't come up often, especially for the price I paid.
IMO a cylinder sleeve is only a good idea when you cannot find a replacement block. Google tells me the Pontiac 261 block is the same as the big six in Chevy trucks of the same era, but I suspect those are pretty thin on the ground too. So with that in mind, it sounds like you need to sleeve that block!
Canadian Pontiacs 50s into 60s were Chevy frames & drivelines with Pontiac skins on them. Look at photos of 59 Pontiacs (first wide tracks) and you can see the difference in where the USA Bonneville wheels are vs. the Laurentian and such from Canada.
Engine wise... this means all Pontiac base inline 6's from this era are Chevy engines. Maybe they did some goofy little things to differentiate (i.e., truck engine with a head you couldn't get in USA as some say for some years). This also holds true for the GMC trucks of this era in Canada --we didn't get the V6 as per USA.
So it depends... a 261 might be tricky to get, but inline sixes are getting replaced with V8/LS in the vast majority of projects and while not that many 50s Pontiacs are getting rebuilt (or sitting around in junkyards) you are talking nearly 20 years of trucks as donors.
If it doesn't have to be a 261, but does have to be that generation of inline 6 (i.e., not the 62 and later design) I have seen more examples running in old grain trucks and such than anywhere else and you could buy the running truck cheaper than getting your engine sleeved, take out the engine and sell the grain truck...
Sleeves aren't all evil by the way. My dad hates them but has run a few in his work truck fleet for many miles with no issue related to the sleeve. Nobody knows it's sleeved but you and the machinist...