Your standard 235 Chevy truck engine should have an aluminium timing gear. Aluminium is stronger, fibre gears are quieter. You can adapt HD straight cut steel gears for a 4 cyl. Pontiac "Iron Duke". It depends on the end use for your engine. If it is a street engine with a mild cam and stronger valve springs the standard aliminium gear should be fine. I believe any 235/261 other than stock would benefit from an after market dampener. Both these items are for reliability. You can build your engine with the stock parts if you want, but stronger gears and an improved dampener are insurance for your "investment". What other mods are you going to do?