I was lucky to find some knuckle heads that I'd like to put on pan cases.
None of my pan cylinders top lip will fit the recess in the heads. Is this because the 74 and 61 heads were made in two diameters?

I'd order new knuckle 61 cylinders but there is so little dimensional info on these, i'd be reluctant to send them the $500.

Second question;

Are the rods a different length in a 61 ?

 

this is only done by someone with vast experience and engine mechanical ability

if your pan is 1963 to 1965 you have an out side oil line to feed the knuckel top BUT ---- pans / knuckels rods changed in 1941 on to 7.440 long and pistons are a thing unless you are building a stroker - the top end oil will over whelm the knuck and it will Pour oil out onto the rest of the motor all the time its running ( did i say all the time its running ) -

best is to forget this idea seen it done but not a novis to go after NOT saying you are but if your asking what your asking you do not know what needs to be done and how to do it - i would not convert a pan to do this it would never go away in my shop i would be stuck with it forever

 

Oil to head I can restrict. Done many times down here.

Right now I've got to figure ;
None of my pan cylinders top lip will fit the recess in the heads. Is this because the 74 and 61 heads were made in two lip diameters?
Is lip called "fire ring"?

 

first picture is a pan set installed and a 74 inch knuck next to it - NO lip // firering

second picture is a knuck jug length 5.540 or about

third is the same pan jug shown in first picture its 1/4 inch shorther -