I have a 73 block in a 67 useing 67 mounts and perches.I bolted a strap of iron to the 3 hole block and welded the motor in.Now that im restoring this car I want it done the right way. Can I drill and tap my bosses on the block or should I use adaptor straps? I looked at the straps in classic but don't understand how they work with only 4 holes.
I have a '73 455 block in my car and all 5 engine mount holes were drilled and tapped. If your block is also a '73, it should be the same. I thought that '76 was the conversion year from 5 to only 3 holes (and not the 2 needed for FGF's).
If not, you can used the adapter plates (probably easier) or drill and tap the other two holes.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
I just checked and my date code is K187. My block casting # is XX481988. On one side below the heads it says GM-5XX. on the other is XX400.by the front is xr81596. Is this a block that was cast in 67 and not used untill 73?
Nope. 481988 is a 1971-1975 400 casting. Look again at the casting date and engine code. There are no XR code 481988 in my reference materials. XR were 326, 350 and 301, and there should be one or two more numerals in the engine unit number.
You have a date that doesn't coordinate with the casting, and a stamped code that does not coordinate with displacement and casting.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
The "XX" blocks are the later castings upgraded for use in the '78 and '79 "performance" cars. They bear the same "988" casting number, but the date code will be as shown. They also have the heavier bulkheads of the earlier blocks, a weak "link" found in the '76-'77 "557" blocks. Typically, the "extra" bolt holes for the early mounts are not drilled, but the bosses ARE there, unlike the 557.
In answer to the question regarding the bolt bosses, yes, they can be drilled and tapped (3/4 - 1" deep, 7/16-14 thread, use a "bottom" tap to finish the threads). Care must be taken to properly align the holes perpendicular to the crankshaft centerline and "level" (parallel) with the pan rail. The holes must also be properly chamfered. The help of a skilled machinist is advised if you're even a LITTLE "nerveous" about it.
