pulled both heads off today.

the 6 bolt shows some sings of hone marks, but... one cylinder's ridge begins where i assume the 2nd ring should be.... possible missing top ring... there appears to be no damage associated with a broken ring, though.

also, running my finger up the length of some of the bores, i can feel variances in width, but there are no score marks to indicate overheating.

the 8 bolt motor is nice and even, but is obviously of higher mileage. the head is approximately 1.25mm thinner than the carbie head - is this more than it should be?

as right now i don't want major expense, i think it best that i just wait for a good used 6 bolt motor that i can bolt straight in... about to get on the phone to get some parts prices, though.

You really ought to be getting some precision measuring stuff... Granted, you can feel a ring groove, but you can't feel a hole that is out of round by 1/1000 inch. When I tore my Jag engine apart, I found that all the cylinders were about 5/1000 longer than they were wide. Easily enough to screw an engine, but definitely not enough to feel by hand...

You'd probably be OK with either engine the way they are, but as long as you ahve it all apart, you might as well take some exact measurements.

-Matt

Another thing.... Where are you located? I have a '72 injected 164 with a decent motor... I'm fixin' to either sell it, or part it out. Its a good runner needing a bit of tlc to be a good driver. Located in northern Colorado.

-Matt

How do you know it's high mileage? Pull them both apart & see how worn they really are. What you are looking for is how much wear the topside of the top ring groove has.