I use the ball end of a small ball peen hammer (a ball bearing works, but I end up hitting my fingers) to cut one bolt hole on a too big piece of gasket material. Then put a bolt through that hole in the gasket and into (or through) the casting, snugging the bolt to hold the gasket in place. Then cut a second bolt hole (furthest from the first bolt is best) using the same procedure. Now that the gasket is held in place use the ball end of the hammer to cut any additional holes and the flat end of the hammer head to cut the rest of the gasket.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.