I have a 3800 Series 2 from a 2002 F-body, with a manual 5 speed. I wish to swap out the t-5 for something stronger. I am putting a Grand national turbo on the 3.8. The engine is going into a 80 Chevy Monza Spyder. I also have a TKO-500, but it does not direct fit to the 3800 bell housing at all. What options do I have? Search results in many ideas, some success, but little hard data. Thanks!

 

I bet this question would get really simple if you reviewed differences of the front end of each transmission and measured some stuff.

Bellhousing to block bolt pattern.
Trans. to bellhousing bolt pattern.
Trans. to bellhousing alignment registers.
Bellhousing to block alignment registers.
Pilot tip to bearing sizing, and depth.
Maindrive spline to clutch disc hub.
Maindrive length vs. bellhousing depth.

Everything can be made to work with everything.

Last I checked, the TKO has been made to bolt to Ford T5 bell housings.
And the 95 and newer 3800 F-body had a Ford pattern at the bellhousing too.

So more detail and pics can only help.

 

That T5 has the 26-spline input, but a 3.75:1 first gear. You might swap in the Ford 2.95 gear set, which might require a Mustang clutch disc, but it's still nowhere near the strength of a TKO.
You're stuck with the bellhousing you have, it may need machining to accept a TKO. It's easy to drill and tap the bellhousing to accept various transmission bolt patterns. If the TKO input is longer, a flat billet plate between the TKO and the bell is your best solution, and easily drilled with both the bolt pattern of the TKO as well as that of the bellhousing.
The main thing is keeping the input centerline perfectly aligned to the crankshaft centerline, both horizontally and vertically.
That v6 is the L36, you really should get the L67 crank, rods, and pistons.