Hello I am installing an ls7 and 700r4 in my 68 c3 . I purchased Top Flights mount kit #75914 and the bolts that pass through the mount to frame will not fit holes are off about 1/2 bolt diameter . Frame measures correctly as per GM specifications. I contacted Top Fight and they recommended this forum .I would appreciate any input THANKS.

 

mbuskirk
Are you talking about the engine mounts?
Are you trying to find out what size bolts were used for that?

IF SO, my 68 AIM says the engine mounting bolt are 3817224. Per ZIP corvette these are the GM bolts:

Original style 7/16-20 x 3 3/4" zinc plated "UR" headmark bolts for attaching engine mount to frame blacket. Correct for 1963-1965 Corvette. Includes (2) bolts, (2) nuts, and (4) washers to complete engine mount installation.(GM Part 3817224)
https://www.zip-corvette.com/63-65-e...s-correct.html

 

Welcome to the Forum

You mean one of these kits?
https://www.topflightautomotive.com/...ine-mount-set/

Why not use ICT Billet adapters, and Moroso solid (SBC) engine mounts? That seems to be the go-to solution for most of the LS swaps on this site, and what I'm using for both of mine.

Unfortunately, our search feature is mostly broken right now. You might have better luck finding threads on this Forum using DuckDuckGo or Google. Here's one I had saved:
https://www.corvetteforum.com/forums...completed.html

Please post some photos!

 

If it's vertical on the engine side mounts. You need to put the engine in and then adjust your transmission up or down to run the bolts through.

I ran a 700r4 for years, but they have to be highly modified to handle any amount of power

 

the bolts that pass through the mount to frame will not fit holes are off about 1/2 bolt diameter . Frame measures correctly as per GM specifications.

Being a 1968 frame I don't know what you actually measured, but I would tend to say that your frame is warped over the years or someone jacked up the car under the front cross brace. I don't think that it would be a problem using a dremel bit to elongate the existing hole. Or cut off those mount raised arms and reweld in the correct for your position.

Attaching the phoney tranny mount to the cross member. I would buy the complete tranny cross member from some place like G-Force for the TKO/700R4. It makes routing the exaust so much easier because the pipes pass under and not through it.

Again I will say that stock 700R4 are very weak. Even the so called updated to 450 hp just die the first day. I bought the 800 hp version with a 9.5 inch Vigilante 3800 stall after blowing a 5 lockup clutch TC. The vigilante was so efficient that it doest need the lockup function. Out cruising it would run withing a couple hundred of rpm of lockup at say 70 mph. My 427 just smoked the lockup clutch by going WOT in a non kick down 4th gear OD.

You will also find out that 700R4 have bad gear spacing. First is way to low and a big jump to second. I bought a 5000 rpm WOT shift govenor to short shift the 1-2 to keep from leaving 100 yard black marks. I went to 345 width rear tires is search of traction and finally gave up and went to a 5 speed. The 700R4's were an expensive experiment.

https://www.summitracing.com/parts/s...QaAkzPEALw_wcB

 

Welcome to the Corvette Forum mbuskirk!

This is the right place to be if you have either questions or issues with a Corvette. You might need some of these guys getting the LS7 working in your C3.