The MG-A "B" series (3 main bearing) engine, found in found in MG A's early B's, metros and other british cars, and, in some India automobiles, is very similar to our J 13 engines, but they're not exact. The J13 block is about one inch or so shorter (verticle) and so, the rods are too. I think the blocks are the same length. If anyone has the measurements to the J13 crank, I can measure my MGA crank and compare. If they are the same, brand new forged steel crankshafts are avalible from Moss Motors for $795. The heads may be the same too. When I compare my L520 engine and MGA engine, the heads look identical. The only difference is in the way the valve covers are attached. The MG uses two threaded posts coming off the rockershaft pedestals vs the J13 valve cover attaches with a series of screws around the periphal edges of the valve cover. If they are the same, new aluminum alloy heads are avalible too, from many of the British carpart suppliers. Moss price is $1395, assembled. Cross-flow heads are avalible too, but more $$. I think the heads are made by Pierce Manifolds, somewhere here in the US. Moss Motors is a huge supplier of British car parts, located in California. They're Ph # is 800-667-7872. Sprite and Midget engine parts are probably too small and won't fit the J13. They are British "A" series engines, with cc range of 850cc to 1300cc. Smaller cranks, rods, heads etc. I'm no expert,just an owner of a few old cars, but hopfully the above info is correct.