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Can't help with the engine swap in a 69 cause I don't know anything about the vans older then 75. Feel free to send the 300 my way. I like the 300's much better then the 302!!
But the answer is yes to the 300 transmission and bellhousing fitting the 302. But you can't use the 300 flywheel. The 300 is a zero imbalance flywheel and your 87 302 needs a 50 oz. imbalance flywheel. You'll need to find one for the 302 that matches the tooth count of the 300's flywheel ( most likely a 164T ) and the correct imbalance for 87 302. And don't forget to use the block spacer plate off the 300.
Oh yea since your 302 was an auto, make sure to install a pilot bearing/bushing. And don't use the starter off your 302. Use the one off the 300. The auto and manual transmission starters have a different nose assembly on them.