Your best bet for a swap would be a 5.0 and AOD transmission,all the externals from your 289 will swap over to the 5.0 aka 302 and for cruising the AOD will help with better MPG,best years are 1988-93 these are roller cam engines and the AOD's have the better lubrication upgrades and improved valve body and are still non-computer for easier hookup.You might check with the builder you mentioned usually you can use your 289 as a core and expect to pay about $100 more for the later roller style 302.
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