If the head is removed you will know immediately if it's a 261 by the 3 pairs of small holes in the deck but bring a caliper to determine if it's been punched out. 3.830" would be .080" over and the end of the road for boring. All Canadian Pontiac's with a 261 had the 848 head drilled by GM of Canada (note that the holes are on a 12 degree angle into the water jacket), bypass oiling, hydraulic lifters, and a fiber timing gear. Look for green paint. Some are alpine green like US engines but I've seen several with a dark olive color. Good luck.
