Question on driveshaft slip yoke clearance..

[68gmsee]

I'm going to get a crate motor for my 69 Chevy (350/350) and was wondering how much clearance is needed from the back of the transmission to the end of the slip yoke for in and out movement...

The slip yoke has about 2-1/2 inches or more of exposed metal and it seems to me that it is barely catching the back of the output shaft. I'm thinking of sliding the motor back about an 1-1/2 in. and that would bgive me about 1 inch of in and out movement.

Thanks.