Did you find out if it is a B20?

Many moons ago when I was a cash strapped teenage apprentice, I found a Penta shortblock at a wreckers. It was seized up from rust, but it had the penta timing cover on it + a good flywheel. The wreckers thought I was a moron for paying $20 for it but when I got it home I was pleased to find that it did have an iron cam gear in it. When I pulled the sump off, it looked good inside, I pulled the crank & found it to be rust free + the bearings where great. Although the bore was rusted, I noted it had no lip, so I put some kero & phosphoric acid in it, let it sit for a few days, then the pistons where able to be knocked downwards easily. I then ground the rust out of the top side of the bores, slid the pistons out, inspected the top ring groove & found them to be great! Next, I took my old thickwall B18 to the machine shop & got it bored & honed out to standard B20, reassembled it with a new set of rings of the generic variety & reused the orignal crank, rods, pistons, bigends & main bearings from the penta. The only really problem I had was that the penta motor was an 8-bolter & I actually had to grind some clearance in to the crankcase for the big rods to clear. It was one of the cheapest motors I ever built & I got many years out of it.