It’s not a slip fit, it’s an interference fit for certain. Also, I I will give you my two cents here, and you can take it with how ever many grains of salt as you wish, lol. I would not heat this balancer. The 235/261 balancer is essentially comprised of two parts the hub and the balancer (not including the pully, three including the pully). The two parts are riveted together with a formed rubber spacer in between the two parts. It’s pretty durable. I don't know what happens to the now 60 year old rubber spacer when its heated in an oven. Might be ok, then again, it might not. Why chance it.
With the crank drilled and tapped, you really should not need to do that. I have rebuilt a couple dozen of these motors over the years and not once have I ever heated a balancer to get it on and I have never had a failure. so I think you should just install it with the proper tool, install a balancer bolt, and you should be good to go!
