Just look & see all those 5.0 Rustangs had T-5 trans,they can take a bit of abuse from a V-8 302.
Sure they all will break after you keep beating on them.
There are world class T5's which are better.
But honestly,your 250 6 will not put a beating on the T5 like those Fox body mustang guys put them through.
They (fox body mustangs) have what you call recipe suspensions,put a few upgrades of rear suspension upgrades ,slicks,or sticky DR's & the run 1.6 60 ft times,which is pretty hard on those T-5's but they still lasted a short while.
Like I stated earlier,,,I don't think you will put a beating on a T5 trans like those mustangs do,,,,unless you get serious about drag racing your car,that would be a different story .
For an everyday driver & reasonable price,(I assume you dont have an endless bank account) The T5 is a very good trans,,,but if you beat on them,run slicks & side step the clutch @ 5000 RPM,just like almost any trans, they will eventually break.
A T5 from a V-8 application will be a better choice.
I used a couple T50 5 speed trans from a Chevy Monza(4 ,cyl models),super low 1st gear,like .95 OD in my Camaro 250 6 ,they would have lasted a long time if I did not beat on them.
Bought those from junkyard cars. Made them look like a 3 speed(hung a couple linkage rods on the outside) so I got them for a lower price $75 ,this was many years ago.
This was also the time I got the best mileage w/those tranys,21-22 MPG.
W/the T-5 you can cut @ weld & reposition a shifter handle where you need it. Because the shifter location will be a bit further back than w/a muncie.
With todays gas prices, you should get a trans & take advantage of one w/an OD.
MBHD
