possible to bolt gmc straight six bellhousing to IH trans?

a t-18 or 19

 

Those numbers you give are from an independent transmission manufacturer. Other than for their farm tractors International didn't make over the road transmissions. Do you see "Spicer" or "Dana" or "Nuprocess" anywhere on the exterior of the transmission case? Three or four speed? Floor or column shift? Length of the tail shaft? When you get that just look for an adapter from the bell housing bolt pattern you now have to the bolt pattern of the transmission you propose to use. I'm sure you'll have to do more accommodating for the main shaft length too.
Normbc9

 

thanks for response dont have vehicle yet
just wondering if it will be a direct drop in

 

I believe the T-18 and T-19 were made by Borg Warner. Keep in mind the bolt holes are only one part of the equation. You would also have to contend with the input shaft/bearing retainer. Ford, Jeep, and IHC used this transmission and there are differences.

These transmissions were top shifters.

T19s in IHCs had a wide ratio, whereas the same transmission in Fords had a close ratio (higher first gear).

The T18s used in early to mid 70s Jeeps had a close ratio.