I believe you can check chain stretch by rotating the engine to 45° BTDC on the #1 cylinder compression stroke. In this position, you should be able to insert the 6mm (?) lock pins into camshaft flanges. If not, turn the engine very slowly until the pins can be inserted, and read how far off the timing indicator is (for example, if the pins will insert at 42° BTDC, the chain may be stretched 3 degrees). The problem is, I believe that worn or damaged chain rails can skew this reading... the chain could be fine, new rails may pull the timing back into spec.
