The question of rebuilding a 6cyl as opposed to switching to a 350 seems to come up a lot. Or in this case rebuilding a 292 as opposed to rebuilding a 350. You've got that 350 far enough apart and possible valve job anyway.
I used two price sources. Speed-o-motive has machine prices on their web site and Kragen (Parts America) has parts prices on theirs.
Cylinder boring & hone - $50/cyl...........6=$300 8=$400
Surface block $40 each side................6=$40 8=$80
Cut head for Hard valve seats $75/hd....6=$75 8=$150
Valve seats....................................need 6 need 8
Cut for oversize valves......$75/hd........6=$75 8=$150
New valves...same for 6 or 8..............need 12..need 16
Grind crank.......................................6=$95 8=$95
Magniflux crank.................................6=$45 8=$45
Resize rods....$9.50/ea.......................6=$56 8=$76
Hang rods on pistons...$7/ea...............6=$42 8=$56
Balance engine..................................6=$125 8=$150
As you can see, most machine work cost is in the setup. More pieces, more setups, more surfaces and more costs.
Speed-o-motive has several engine kits. Here are two, only to show difference between 292 and 350.
A "Deluxe Master Engine Kit" includes; cast piston, rings, rod & main bearings, oil pump, timing gears, cam & lifters and gasket set.
292 is $475 350 is $330
"Crank Kit" includes; piston, rings, rods, R & M bearings and crankshaft.
292 is $510 350 is $470
The 292 prices are higher in engine kits for all the outfits that I've checked, if they even have 292 kits at all. Most of the difference seems to be in the pistons. Six, 292 piston prices are well above eight, 350 pistons. Timing gears for a 292 are twice stock 350 and still above average 350 double rollers.
Kragen 292 and 350 prices
Pistons, cast Clevite........................6/$28=$169 8=$98
......... stock LPG 9:1pistons..............6/$45=$270 8=$0 already at 9:1
Rings, cast iron...............................6=$52 8=$20
Cam bearings..................................6=$26 8=$24
Main bearings.................................6=$35 8=$30
Rod bearings-same part# $3.19/ea......6=$19.14 8=$25.52
Oil pump........................................6=$18 8=$18
Brass freeze plugs.............................6=$8 8=$9
gasket set......................................6=$48 8=$46
As you can see, they will clean your clock on the pistons. The other parts are not that much different if you stay stock. I forgot to check cam prices. Stock 6cyl cams are usually higher than stock 8cyl. Hyd lifters are the same. You just need 12 or 16.
Higher parts prices balance lower machine prices. Of course your local machine shop may have other ideas.
If you don't let high performance chrome plated muffler bearings and delusions of racing a Viper cloud your judgement, you can probably get by cheaper with a stock 292 rebuild.
One other thing to remember. If you have to bore and get new pistons for either, you're getting up close to 350 crate motor prices. My one year old Classic Industries catalog has reman prices of $1380 for a 292 and $1200 for a 350. That option changes if you have to add core($250) and shipping, because you don't live near a similar outfit.
