This is a vital component, and while it won't destroy the engine if the cap pops off, it won't run.
Might consider taking a few minutes and doing it right.
Go to any local hardware store and get an Irwin tap/bit set for the next biggest size screw. The pack comes with the correct drill bit and a decent quality tap (startng tap I think). Probably cost something like $7-8.
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If the distributor base is currently tapped for a 10-32 screw for example, get the 12-24 kit. If it's a 12-24 screw get a 1/4"- 20 kit.
Don't forget to pick up a couple of new (bigger sized) hold down screws - of the same length.
The base is probably made of cast aluminum and, if you use a few drop sof 3 in1 oil, it should drill and tap like butter. You don't even need to buy a tap handle; just use a small adjustable wrench.
You may need to ream out the holes in the plastic cap to accept the new/larger screw. Since the bit that comes in the kit will be sized for tapping, you'll need to either wiggle it around a bit or use a slightly larger bit than the tap.