Why wouldn't you use a truck motor?

: Hell, this is probably even a Mexican block!

One thing to be aware of though, is that 73-76 blocks have a .019 higher deck hight, but you can just have it decked and the extra .019 removed so you don't have any other considerations over a "normal" 302 block. If it's a mexican block, I'd definatley use it!

The extra deck hight will lower the compression and change pushrod length, but those can be easily overcome with aftermarket parts if you don't want to get the block decked.
HTH
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66 coupe 5.0/T5, home-brewed power 4 wheel disc setup, 350hp+, looks like it belongs in 1968