WC waste to cast iron soil pipe

[R_Deckard]

Hi all,
I'm replacing our toilet in a 1930s building, the old clay waste (standard 110) is held in the cast iron soil pipe opening with tons of resin (inside dia. of cast iron opening looks around 140mm).
Should I avoid taking out the old resin and instead angle grind the clay pipe off? Would a standard pan connector fit into the inside of the clay pipe?

My connector could probably fit into 97mm dia.)
Anything else I'm not considering?
Thanks in advance!

 

[muggles]

Would this help? https://www.toolstation.com/flexible-adaptor-clay-to-pvc/p54240

Might be lead rather than resin in the joint, have you tried scraping it?

 

[jeff the gasman]

Looks like a twin stack installation and very little room before the boss off the top.
Whatever you do good luck.