Driveshaft shortening q's

[C15_Sierra]

I'm finally getting around to shortening the driveshaft on my C15 LWB...305/TH350 went out, 5.3/4L60E going in. Motor mount adapters position the motor towards the rear 1", plus with the added length of the motor/tranny, I know I need to shorten the stock shaft

When I got the tranny buttoned up, I inserted the yoke about 2/3 of the way in (give myself some error room) and matched up where the carrier bearing holes were on the bracket, since I have a 2-pc driveshaft. Is this the proper way to measure a 2-piece? I figured if I only shortened the shaft in between the tranny and the carrier bearing, I would be good to go the rest of the way (basically mimicking the stock fit). But, since this is my first time, I'm measuring 5 times, asking the forums, and praying that I didn't screw anything up before doing something as irreversible as shortening the d/shaft.

Btw, by that method, I measured 4.5" as the length needed to come off - does that sound plausible to you LS swappers? Not sure which tailshaft size TH350 came out, motor/tranny are long gone (were originally from a '79 Camaro if that helps)

Any other tricks I should know, or just man the **** up and go to town?