Will GM 200r4 work with factory floor shift location?

No,no Treblig. Don't be bothered at all. This is all great info. I keep finding conflicting information on the web regarding whether the measurement is 27 11/16" or 28 1/4". It does make a difference at the crossmember. Interestingly, if I subtract the thickness of the adapter ring that allows the bellhousing to bolt to the front of the modified 200R4, I get the 27 3/4" you have. Not being able to get around that extra 1/2" length with my set-up, It looks like I will be doing even more cutting at the crossmember than I had originally anticipated.

There are some variances in the production tolerances in these cars, but likely not an extra 1/2 " in where the trans will end up. I knew I would be doing some modifications at the crossmember. My goal has always been to minimize the cuts, weld up any "holes" that result with concave plates to reinforce the area and build a very structurally strong bolt-on crossmember that also serves as the rear transmission mount. I will attempt something similar to the Hotchkis piece, but with the square, u-shaped attaching points that bolt to the factory crossmember like the original one does.

If after looking at the results of that and your collective opinions are that it needs to be reinforced even more, I will have to add some extra reinforcement in some way yet to be determined. The floor pan is an integral part of the actual stamped steel crossmember to begin with, and its just spot welded to the crossmember in a few spots. Treblig's addition of the steel plates to fill the gaps between the floor and the crossmember is going in the right direction. I used the US Cartool Subframe connectors that weld to the floor in my car, and they made an incredible difference in the car's rigidity. Following that lead, I will finish welding the torsion bar crossmember solidly to the floor from one side to the other as part of the first phase of strengthening entire assembly.

If it weren't for not having the components available to measure for an accurate torque converter "depth" right off the bat. This bolt-on bellhousing system has incredibly easy so far, All I did was bolt it on. I did spend 5 minutes chamfering a small 3" by 1/2" edge on the lower inside lip of the bell just under the input shaft side of the housing ( the torque converter just touched it there), and I shortened some bolts by a few threads..

The bottom line is that the challenge and the real truth about installing ANY overdrive install in these old cars is that you HAVE to make the modifications to the crossmember and fab the rear trans mount.

((The only exception I know of is Jamie Passon's new 5 speed...BTW, yesterday he said he's shipping mine for my 1970 "Cuda after this weekend. My 1970, number's 440-6 'Cuda is a car that I would never consider doing any crossmember modifications to. For those following that 5-speed release, I was #18 on the list. I'll add some e-body pic of the car for those interested in such things. I digress, sorry a-body forum members.))

Another "anticipated benefit to the bolt on housing is that the smaller size of the bellhousing in the firewall area, "should" make the rest of the install relatively simple by allowing extra room for exhaust and whatever else goes through that area.

Getting back to measuring the transmission length, I used a large L-shaped straight edge/ 90 degree square and a level to make sure I was getting a parallel measurement for the most accurate length measurement I could get from the face of the bellhousing to the end of the tailshaft where the seal goes.

I came up with 28 1/4". I also measured the adapter ring that goes between the transmission and the bellhousing and found it to be exactly 1/2" thick.

Once I have the transmission up in the car, I will see just how much of the crossmember needs to be modified. I'm sure your predictions will not be far off Treblig. I do want the cuts to be simple in nature and reinforced where the cuts are being made to make room for the transmission. I'm also hoping that by using a design similar to what Hotchkis used, and welding the crossmember solidly to the floor for it's entire length will make it even stronger than it is now.