273 Timing Marks

Its about 65 Degrees or so.

However, You can do this yourself with a positive stop installed in the #1 spark plug hole. Use a standard 318 balancer, they are the same as 273, you might need to elongate one hole in the crank pulley to allow installation of all 6 pulley bolts. Install the balancer, check that the TDC mark is pretty far away from being at 0 degrees and install the positive stop. Rotate the crank by hand using a wrench until the #1 piston wont move. Mark the balancer where it lines up with the "0" mark on the chain cover. next rotate the engine around the opposite direction until the #1 piston stops any further movement. Mark the balancer where it lines up the "0" mark on the chain cover. Rotate away from the stop - the opposite way partially - and remove the positive stop. Rotate the engine until you can see your two marks on the balancer. Exactly in the middle of those marks is your new TDC mark for the balancer, you can file a mark on it or paint a contrasting stripe in that position. Done. Reinstall the #1 plug, check timing and you are good to go.