It's a crapshoot. Mine fits in my 69 without problem. Others have had to hammer the firewall to get them to fit. The frame mount/engine mount combo seems to play some role. Mine was an orinal 307 car. Try the "search" function at the top of this page and you might find some more detailed info
I didn't think mine would fit..at first. I replaced my engine with a crate 385 fastburn. And I used subframe connectors. But after doing the subframe alignment it slipped right in. Tight fit, but it fits. Some guys have to "massage" the firewall just a bit. Very common.
I have a similar setup as yours and the answer is no - it won't fit. There have been folks who have changed the frame mounts and gotten it to work. What I did was have my old breaker point distributor rebuilt and upgraded to HEI. It looks stock, fits, and works. Check it out at http://www.davessmallbodyheis.com
I'm shootin from the hip here and some will disagree with what I'm saying, but I've never had a problem fitting an HEI to a first gen with a small block unless the frame and or motor mounts have been moved. If it doesn't fit at all (I mean you need an inch or so) then the only fix is to move the frame forward or check to see if the motor mount perches are correct or have been moved. If you're in the middle of a resto this is a practical solution. If the car is all together and you don't want to beat on the firewall, then all is not lost if you only need 1/2" or less. The intake manifold on most STOCK applications can be moved forward. The distributor contacts the firewall in these circumstances about 4" or so above the intake opening for the dist. So you don't have to move the intake the whole 1/2" to achieve the 1/2" clearance. 1/4" to 3/8" will do it. If you have port matched your intake then you pretty well have to go with the position that fits the port match. You will find that most first gens will allow a HEI to fit if A) the frame is in the factory aligned position and B) the intake is properly positioned so that the distributor fits perfectly in the machined socket in the block and is centered in the intake hole before the intake is torqued down. I found the B example on my own car when I changed my engine this winter. The previous engine had enough clearance between the firewall and dist. to put a finger between them. After the engine swap (Identical engine and intake, I installed the intake on an engine stand) I found that my distributor touched the firewall????? What gives? I later (after ruining a $60.00 gasket set) found that I could move the intake a considerable amount and still have the distributor fit without a problem. Naturaly it's best to have the dist. centered over the oil pump drive, but I wonder how many cars are running out there with this off a bit forward or backward. I have never seen any reference (other than for machining) to this position of the intake being a critical or measurable fit in any service manual. It's just a matter of plunking it on so the bolts will go in and torque it down. I would suggest you put the intake on the motor and install the HEI before you tighten the bolts. Move the intake forward enough to have a comfortable amount, say 1/4" to 5/16" clearance from the firewall, without having bolt hole interference and torque it down. Don't force the dist forward. There is some clearance between the block and the housing but I wouldn't fit the distributor with any resistance fit at all. If this isn't practical or doesn't provide the clearance you need then I would do what most people do and put a smaller diameter dist in.
Hope this helps.
To get mine to fit I took the carb and dist off and no joke had to swing a sledgehammer as hard as I could to get it to fit. It had about an 1/8" clearance. Talking to the guy at the tranny shop he put a 1/4" spacer between the crossmember and the tranny mount to lower the front of the engine. It gave me just enough room to get it where it needed to be.
fwiw, i had a '68 with a 283, converted from a six using stock mount towers from a nova, no problem with an hei. my current 68 was all original 68 327 stuff, ran an hei with no clearance issues. i now run an msd pro billet, i'm done screwing around with rebuilt factory stuff.
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