Yes I still recommend a block filler - it greatly stiffens the bottom end and has not proven to be any issues with a partial fill and day to day use including towing.
I also have to say there are better block fillers out there than "Hardblock" take a look at some of the two part polymer block fillers that almost resemble epoxy. As the engine block heats and cools and flexes under power cement will break away from the walls and then you will just have a block with cement in it. The polymer fills adhere to the block and you will rip chunks out of the block before it lets go - its a much stronger setup when finished.
HRT,
I have been considering what to use and had at first settled on a polymer for the reasons you mention. I since then have been looking at and thinking that
Metalic-Aggregate Grout specifically Embeco 885 or 636. Looking at the expansion rates they seem to very closely mimic our iron blocks. I thought that since they are used as heavy machinery mounting grouts you would have some experience or tech on them.
The reason I actually started looking into the grouts was that from what I had read at least some of the epoxys got flexible or more pliable at higher engine temps and that it did not expand while curing like a the above grouts do thus not giving it as much "lock-in" when it cures.
When I was trying to draw a consensus on what was working the best it seemed it was all across the board. Some swearing by hardblock other s the grouts some epoxys or even what ever plain old hydraulic cement you could pick up at the industrial store.
Whats your opinion on sleeving all the cylinders for added strength and rigidity? If it were done correctly it would seem it would work well but I have no practical expeirnce with it outside use for cylinder repair.