You said you don't plan to paint 'for a few years'. So I guess you are planning to put the engine back in before that? If you can decide on a color you should go ahead and paint the bay now (assuming you don't plan to pull the block again). Is this a 'driver' paint job? As long as you are not going for show quality, you can probably shoot it yourself and do as good or better than the factory. If you have access to a compressor, you can get a HF gun and some single stage paint inexpensively and have it done.
If you do want to just paint the messed up area.... Your paint code is on the fender tag. Get a clear shot of that an we can figure it out. It's not cheep, but you can order just about any color in spray cans. What year are we looking at? I will say it is very close to my '75 color - T4 cinnamon poly. I found a rust oleum color ' espresso brown' that is very close but not metallic. I did spray correct color in my bay, but used the spray bombs for other areas like floor pans, behind dash etc.