It depends whether you are using the earlier "short" water pump (best idea) or sticking with a 1970 and later "long" water pump.Are you replacing a 6 cyl or a y-block ?
I've got the long pump, '78 block, but I need to drill the timing cover for the dipstick relocation, so I can always swap for the shorter pump during that process. Replacing 239 Y-Block, but I sold the radiator with the engine, because I was planning to buy a new radiator anyhow.
I would use the short pump it will give you much needed clearance,but you also need to use an early balancer and pulleys to match. http://www.ebay.com/itm/1965-1968-P...ash=item1c5fed0d90:g:wTgAAOSwQoFWOmeF&vxp=mtr And http://www.ebay.com/itm/1965-66-SB-...ash=item4aef6ddefd:g:epQAAOxyEoFSVznB&vxp=mtr And http://www.ebay.com/itm/1965-66-SB-...ash=item4aef6ddeec:g:hb4AAOxysstSVzmn&vxp=mtr .
Then this would be the radiator: http://www.ebay.com/itm/67-69-FORD-MUSTANG-TORINO-LTD-L6-V8-3-ROW-TRI-CORE-FULL-ALUMINUM-RACING-RADIATOR-/161289888160?fits=Year:1968|Model:Mustang&hash=item258da061a0:g:2u4AAOSwosFUWVwn&vxp=mtr Then you can tell the parts guys when he asks about belts and hoses "I have a 1968 Mustang with a 289"
Don't forget this ! http://www.jalopyjournal.com/forum/threads/ebay-parts-deal.1007871/#post-11379313
Lots of good ideas using aftermarket radiators but I see no reason why the original radiator wouldn't work, Its size should be more than adequate. My '66 Mustang with a hopped up 289 had what I thought was a tiny radiator and it cooled very well.
Yeah, I don't have the original radiator anymore, sold it with the Y-Block with intentions of buying a new aftermarket radiator.
I'm running the 67-69 Mustang/63-69 Fairlane radiator on mine, specifically a Champion 2-row aluminum one, PN EC340. Couldn't be happier. I just picked up a strip of 1/8"x2" steel and made some side brackets to mount it to the factory bolt holes. Also running a FlexALite 116 16" electric fan.
I'm running '63 Falcon 260 mounts (Anchor PN 2220/2221)... I'm running a T-5 and I found these mounts set the engine a little lower and further forward than the Mustang mounts for extra firewall and bellhousing clearance. Headers are Hedman PN 88400 shorty headers.
Only issue I can see it you are using those mounts you better be using the early "short" water pump".