To make his car just functional with a 302 (not considering ride quality or braking) from what i understand, he will need these:
V8 motor mounts (the engine crossmember is the same)
His car may already have a double hump crossmember for the transmission, but if not he will have to get one for dual exhaust as well as an H-pipe hanger bracket.
A 2 core or larger radiator instead of the one core 4 banger radiator.
A stronger transmission (the 2.3L T-5 doesn't do good under any kind of abuse), but if he feels like driving like a grandma the 4 cyl one will work.
Another good idea is an 8.8" rear axle instead of the stock non-traction lok 7.5" rear end.
He will also need the computer out of the V8.
He will need the instrument cluster out of a V8 donor car because the stock tachometer for the 4 cylinder won't work properly or he can buy an aftermarket tach.
The driveshaft is the same length and can be re-used.
Good ideas for the future after the swap:
The 4 cylinder springs are good for drag racing, but are soft as well as the stock struts/shocks so replacing them would make it handle well. Also the 4 cylinders didn't come with rear sway bars, and adding one at any time will make a huge difference in handling
To convert to the 11" brakes of the 5.0L's he'd have to get new spindles, struts (mounting points are different between the 10" brakes and 11" brakes), i believe master cylinder, calipers and lines.
The A-arms are different, the 5.0L ones are low friction and the 4 cylinder ones are standard.
This is all i can remember right now,
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'84 Mustang 5.0 LX
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'89 Mustang GT
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