I'm doing a 5 speed conversion on my 850 turbo. The car has no radiator. I've got a radiator from an NA auto, which has the trans cooler in the radiator, but not the oil cooler that the turbo cars had.

Since I won't need the trans cooler now that my car is a 5 speed, but I will need an oil cooler, is there any reason I can't just run my oil through the unused transmission cooler in the radiator?

 

You mean besides that fact that the lines won't reach?

 

Given the overall size of a 5 speed conversion project, I'd say getting a couple hoses made longer is the least of my worries, but yes....if I can overcome that obstacle, is there any reason I can't cool my oil through the transmission side?

 

Not a reason at all. The transmission and engine oil coolers are identical except for which side of the radiator they're on. I will say this, though. I would run an external cooler instead. If you have a used radiator, the oil coolers both have failed before and caused serious damage. I had the engine oil side burst and take out my #3 rod bearing. It's not the most common thing but it can be prevented with a more effective external oil cooler for less than 50 bucks.

 

Yes you can use it for an engine oil cooler.
An external is nice in the summer as it isn't adding any heat to your coolant. An "internal" cooler is nice in the winter if you have an automatic as it helps warm up the trans fluid.

NAPA is one source that you can try to see about having the hoses extended. They can custom make hydraulic hoses so they would have compatible hose and the equipment to crimp a leak free fitting.