The Vega 2.3 liter engine has its own bellhousing flange, no other transmission will fit it. Your choices are either the TH250 or TH350. From personal experience, that 2.3l engine won't have enough power to run an overdrive, anyway.
I am not sure if you can get a bellhousing adapter, if so you could adapt a TH700R4 but you'd have to shorten the driveshaft.
As MagicRat said, you'd have to run an external cooler on it. The Vega trans is air cooled and there are no provisions on it for an external cooler, so the radiator does not have a trans cooler internal to it. You might be able to run a later model Monza radiator in it, and run the cooler lines as required.
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1988 9C1 - Modified LM1 @ 275HP/350TQ - TH700R4 - 3.08 8.5" Disc Rear - see it at
http://www.silicon212.org/9c1!
2005 Crown Vic P71 - former AZ DPS - 4.6 liters of pure creamy slothness!
1967 El Camino L79/M20 old school asphalt raper
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