Need frame/tub reference measurment

OK. I'm building a jeep from parts. It's a fiberglass 6 tub in a cj8 frame. I don't know if it should go here or someplace else so mods please move as needed.

Anyway, I need to set the tub on the frame in the correct location. Motor will be a 401 so I don't have much wiggle room. No problem left to right. Front to back, since nothing has ever gone together before I need to make it work.

I need a reference that can be found on a CJ8 frame (not the front spring buckets) I can locate the firewall to. I want to use the motor side of the firewall. I've got a cj5 to reference. But it's a 74 tub on a 76 frame. What I've done is drop a plumb line to reference the rear, top motor mount hole and measure the distance of the plumbline to the firewall. But I would really like to get another measurment to verify. Somthing like the back side of the front cross member to the firewall. Or the shock frame mount on the front axle to the firewall (used a plumb line here as well).

I know it's kinda a strange problem but it's what I got.

And here is a picture of where I am so far.........


I can start a build thread if anyone is interested.

For reference, cj6 tub on a cj8 frame, 401/T18/D20, D44/D60's with 4.56 gears, 4wheel disc, detroit in the front, spool rear. Vented windshield from Spud getting a fairly complete restoration. Full cage. Lots of other little goodies as well. Tires are roller 37's for the build. Gonna paint it like an old military jeep.........kinda. And I don't want it be nearly as high as it is when it's finished.

 

Since the CJ-6 fiberglass tub was made to go on a CJ-6 frame. I would reference that to the CJ-8 frame....meaning the differences in the frames. I would get 76 up CJ V8 motor/frame brackets and put the 401 in the stock location using CJ V8 headers that dump down, not back like the wagoneer. Fit the tub on the frame referencing the first set of body mounts OR the rear of the tub to the CJ-8 frame once you bring it to CJ-5/6/7 rear specs. So for that CJ-8 frame, that means not only cutting off the extra length, but removing the second to last crossmember and welding in a new rear crossmember for the rear tub mounts (the second from last CJ-8 mounts will need to be moved for this). The real issue is locating the tub mounts side to side when jumping the post 76 year mark as the frames widened from the tub back. BUT you have a 76 frame under a 74 tub, so you should have that solved for you. Oh yeah, you will need to use 72 to 81 fenders as well as it looks like you have an 81 CJ-8 frame. Unless you cut off the welded front shock towers and go with the taller 82 to 86 versions.

 

That gives me a lot to think about. Thanks. I was trying to not have to set the motor up to locate the tub. But I guess I'll have to. I'll compare the frame measurments of the 6 and 8 and see what I can figure out. Problem is I have no idea, other than the front of the firewall, what measurments would match up to a stock tub.

I didn't know the CJ fenders changed in 82.

As I was working on the tub, there were 3 sections of metal that made up, for lack of a better description, a subrame. The tub was bolted to the subframe and the subframe was bolted to actual frame. When I took the subframe off,there were sections of rubber, kind of like ribbed conveyor belt, that went the length of the three sections.

Right now the plan is to build 3 new sections, only making them thinner, out of 1.5 square steel, not the orgional 2". Instead of thick rubber body mounts, I was going to use thinner material, say 1/8 to 1/4 thick. So it will be Frame, rubber, subframe, rubber, fiberglass all bolted together.

And I have no plans on cutting the 8 frame in any way. I'm going to use the extra foot of frame on the back of the tub to mount a rear winch, tire rack, etc.