So I am putting together a new motor onto my existing 727 / PTC 9" converter. With the block and tranny bolted together how much clearance should there be between the converter (fully seated onto the tranny pump) and the flexplate? I have read at another site that there should be 1/8 - 1/4" which would mean the vert will slide forward to meet the flexplate, and provide room for converter expansion so the crank thrust surface isn't worn out.

I think mine were less than 1/8" but still had a little gap. I will unbolt the vert and check it but what number am I looking for?

You can put some washers between the flex and the conv
to pick up some more... I like to see about a 1/4 to
5/16.. some use more than that... if its a big torque
engine and you dont have anti ballooning plates you
would want more
EDIT
I run a mid plate.. .090 thick.. that shoves the trans
and conv back .090... also any more than that you
should have the nose of the conv adjusted

think your fine with that. I just measured my vert mount to edge of trans mount flange and its 1/2" right on spec and once mounted back up I have to pull vert 1/8" forward to meet flex plate.

I have check several different brands and sizes of race converter as far as the depth of the converter mounting (7/16 thred size)lugs to the front edge of the bell housing, if see at least 1/2, .500 to 3/4 inch .750 depth using a good straight edge I then consider the converter seated into the pump all the way. As far as the distance from the flex plate to the mounting lugs, I'm think, I have never measured that accurately, a 1/2 to maybe a little more is good I have had one converter that would not pull up flush to the flexplate so I checked around with several of the local Mopar racers as well as on here and they had seen that also. I'm against using washers to space the converter to the flexplate unless you know you have at least the diameter of the fastener, 7/16, engaged into the mounting lugs I have installed a lot of race converters into many different Mopar race cars and I have only seen that once, me thinks that is not normal and should be fixed instead of patched One other thing to check is the front hub on the converter into the crankshaft flange to make sure it is in far enough to support and center it when connected

Without knowing for sure how far the conv will slide
into the crank area you wouldnt really be spacing
the conv back when using the washer... you have a total
distance of where the conv bottoms out on the pump
and where it bottoms out on the crank.. so if the
total distance is short then you either have to space
the trans back or change the nose of the conv so
you gain more space.. if that space is good then
you can leave the conv at the 1/8" from the flex..
hope you see what I'm trying to say about the total
distance

Another PTC vert I have would not bolt to the flexplate because the crank bolts would hit the vert body. That one did not have washers welded on as does another I have so it is back at PTC to find out what is wrong. The other I have is mounted now and engages the crank / flexplate just fine. It also seats well into the tranny pump and is back behind the trans flange maybe 1/2" (didn't measure) but I don't think I have 1/8"+ clearance between the fully seated vert and the flexplate with the trans bolted to the block. I will undo the 4 vert bolts and see just how much of a gap there is (which will allow for expansion) but I ask: How much gap is required?
I suppose that a guy could measure the flexplate and see how far out from the block flange it is and the vert to the trans case before mounting them together, to get the dimension.

I can look in my trans book later to see what the
distance should be

I think there is some confusion as to what the OP is talking about. From what I read, he is pushing the converter back into the pump and he has about 1/8" clearance. If this is the case then the clearance is fine and all he needs to do is pull it forward and bolt it to the flex plate.

The other problem that comes up that Airwoofer mentions is the converter will not pull up flush to the flex plate. This is most often the case with small race converters that use a GM front cover. The indentation around the center of the GM converter is a smaller diameter than the bolt circle of the flex plate to crankshaft bolts. The crank bolts hit the converter and prevent it from fully seating. In this case, if the converter can be pushed back into the pump(indicating there is clearance there) then you can simply use washers to take up the space when the converter is pulled forward again. Keep in mind you do not want to use spacers so large that you space the converter pilot too far back that it is no longer supporting the converter. If you cannot move the converter back into the pump, then you need to clearance the bolt heads or the converter to gain some clearance.

When you push the converter into the trans until it stops you can't assume that what stops the converter is the pump drive hub bottoming in the pump, it could be the converter bowl hitting the pump housing.

Everybody seems to think that if you have more than 1/8" to 1/4" pull up to the flexplate the pump tangs won't be engaged properly and, conversely, that too little pull up means the pump drive hub is close to bottomed but, more likely, it is the bowl contacting the pump casting.

Easy enough to check; with a freshly painted converter, push it in until it stops and spin it...if it's hitting the pump casting the paint will show it. Many pump castings need to be machined for optimal clearance.

The combo ended up at just under 0.100 gap so there is that much float available before the thrust bearing surface sees pressure.