... You have a Blown Head Gasket between those two cylinders. It happened to Me Twice!! As I had 'read', the Head Bolt Torque, for the Boss 351, was "90 Ft/Lbs". WRONG! The Third time of tearing the Heads off, I contacted ARP about the Torque Setting for their Head STUDS for IRON Heads on a IRON Block.
The Answer 130 Ft/Lbs of torque, in the usual pattern and in increasing increments. Never had a Problem since. If You are still using Head BOLTS with the 11:7 C.R., when you pull the Heads, You may think about installing STUDS. When using Studs, You are changing from 'Course' Threads to 'Fine' Threads. Fine threads create a 40% Higher Clamping Force! A Bonus, since Head Bolts Never reach to the Bottom of their Bores and Studs are installed All-the-Way into the threaded bore*... Studs are More Rigid and will help prevent 'Head-Walk', which can also cause blown gaskets. (yes, there are hollow dowls for Alignment, the Studs Help keep position)
Also, those Quench Heads with 'Pop-Up' Pistons AND a .606" Valve Lift... comes into Question! Are there adequate 'Valve Reliefs' cut into the Pistons?
* When one Installs Studs in a Iron Cleveland Block... the 'Instructions' read "Install them 'Finger' tight". I put them In Snug plus a 'Little' pressure and with a Sealant. The WARNING here is... There is a Danger of Breaking into the Water Jacket, should one Mistakenly OVER Torque the Stud into place, as it is at the Bottom of the Bore and pressing against the Cast Iron.
Be Aware.
MJ