If the engine has not been run even though it's 40 years old, be aware that cams and followers need to be bedded in otherwise the cam followers can pick up on the cam and ruin the cam. has it been run in? if not you should run the cam in.
Cam run in process.
coat the cam lobes with special cam lubricant (for running in) but don't put this lube down the bores use ordinary oil there
Run the engine 2,500 rpm for 20 min and don't let it idle apart from starting and shutting down.
This is an important process for new cams, you can check this out on cam suppliers website on how to run a cam in.
If you are just starting to check it fires and no bad noises for literally a few seconds then that should be ok.