Are you sure you need that long of a chain? If the chain is long enough to wrap around the big chainring/big cog + 2 links then it should be good.

But I know what you mean about long chainstays on older bikes. It certainly is possible you need a longer chain.

Call around to shops and see if they have any spare 6/7/8 sp links leftover... most chain replacements in shops wind up leaving a few links left over and the shop might give them to you or sell them for very cheap if you buy a new chain from them.