Difference between big block and small block motor mount perches???

[FLYNAVY30]

I just ordered my LS swap kit from BRP Muscle Rods.....


My question is, do I need to order the small block frame perches because it appears that my factory big block has 4 bolts as opposed to the single bolt mounting you can see in this kit.....or do the supplied brackets mount directly to the frame with a single bolt, eliminating the factory perches? Unfortunately the included directions arent terribly precise.

Yes the kit is meant for a half ton truck, but nobody makes an LS kit specifically for the 3/4 tons.

Thanks

[BR3W CITY]

4 bolt holes goes on your engine, the bushing fits into the smaller bracket with a bolt, the single bolt side goes to the frame. I imagine this removes the perches. This is ONLY from seeing random pictures. I didn't use the kit so don't quote me on this one.

[FLYNAVY30]

Ok, I appreciate the help....motor comes out on Friday so I'll know for sure then. From looking at pics of everyone else's builds, it looks like the set up I purchased eliminates the perches entirely and bolts directly to the frame.

[FLYNAVY30]

having taken the motor out, it looks like I do in fact need the 1/2 perches to bolt the new LS, single bolt mount to. Either that or I can attempt to drill my big block perches to match the mounting hole in the small block pieces, if I can find some measurements as to where to drill the hole....

[FLYNAVY30]

here is a picture of my big block perches, with the 3 holes as opposed to the small block perches with 1 hole that would mount up to my brackets. I would just get a set of the small block perches, but those only have 3 bolt holes that attach it to the frame, and as you can see, the big block perches have 4.

So at the moment, Im stuck....

[tinydb84]

What year is your truck? The mount towers with one hole are pre 73 I believe. You can order those and redrill the frame for any missing holes.

Looking at your mounts in the first pic, I would see if you can just drill a hole in the center of your towers and try bolting it up

[FLYNAVY30]

Yea we considered that....just concerned about drilling the hole accurately so everything lines up

[crazy longhorn]

1/2 , or 3/4, does not matter on the frame stands.... BB/sb/ I 6 is the difference. From what I see, you have a 72 BB truck? I cant really give advice on the stands & mounts that you have....you might talk with the manufacture, as to what stand/position that they fit. 10-30 series, on the 67 -72 trucks, are specific to engine size....in other words, if the mounts you purchased, were meant to fit a sb stand, that is what you need? Be aware that the I 6 /250 stands, set the engine in the rear position....sb stands, in the forward position (3 1/2" C to C difference) between the 2 sets of stands. The BB stands come somewhere in the middle of these to spots, & also mount the engine a tad higher. Hope that helps....any ?, fire em back Longhorn

[FLYNAVY30]

thanks Long Horn....ended up ordering the CPP mounts that eliminate the frame stands entirely....they should be here this week, we'll see how they work

[crazy longhorn]

I have been a welder/fab nut , for many yrs....I don't see a 'bolt in swap"? My 5.3 sets in, 1 " forward from I 6 inline spot, & very tight to the firewall. In the mid 90's, she had the firewall clearanced (around the heads), for a BB Olds that set that tight to the rear. Hell on wheels, with a 461 Olds, mild cam, backyard port job & an 800 DP carb, on a Torker intake....but only 6-7 mpg, on a loose verter & low gears, fun but (ouch)! The carberated 5.3 is still running the 6 spd Richmond trans, hooked to a 55 chev bell(7th bolt on the top of the bell). A little "finish up', & she is ready to go....but old rods , are never done....you just add as you go. Longhorn